6.7: Detailed Figure Descriptions

Figure 6.2.1 Rodinia

This circular paleogeographic reconstruction shows the Rodinia supercontinent as it may have appeared about 750 million years ago (Ma), during the Neoproterozoic era. The supercontinent is composed of multiple continental blocks labeled with their modern names. These include:

• Laurentia at the center
• East Antarctica, Australia, South China, Siberia, India, and Madagascar to the west and north
• Baltica, Amazonia, West Africa, Rio Plata, and Kalahari surrounding Laurentia on the south and east
• Congo–São Francisco in the southwestern sector

All landmasses are shown in brown against a blue ocean background. The map provides a simplified visualization of tectonic reconstructions used in geology to understand ancient plate configurations and supercontinent cycles.

Figure 6.2.2 A Diagrammatic Passive Margin

This simplified diagram shows a passive margin along the western North American continent. From left to right we see the ocean depicted above a thin layer of sediment, which rests on a thicker oceanic crust above a still thicker mantle region. The middle of the diagram shows the sediments quickly increasing in thickness as the ocean layer thins. The oceanic crust gives way as the continental crust thrust upward, pushing the mantle downward. When we reach the right side of the diagram the ocean has receded and the continental crust takes up most of the vertical space. A very thin layer of sediment overlays the continental crust, and the mantle has thickened below it.

Figure 6.2.3 Distribution of Precambrian Rocks

This detailed diagram from the California Geological Survey displays a statewide geologic map with a corresponding correlation chart of map units based on age and rock type.

Highlighed are precambian Rocks (older than 541 million years). These are some of the oldest rocks in California, representing the ancient continental basement that formed long before most tectonic accretion events that built the rest of the state’s geology.  Precambrian rocks are not widespread across California. They are restricted to specific regions, mainly: Southeastern California, Eastern California, east of the Sierra Nevada.

• Precambrian plutonic rocks . These rocks are shown in the southeastern part of California, concentrated in the southeastern corner of the state. They appear as isolated exposures surrounded by younger rock units. The map indicates that these rocks are older than 541 million years and are limited in geographic extent.
• Precambrian metamorphic rocks. These rocks are shown in eastern California, primarily east of the Sierra Nevada, including ranges near Death Valley and the White–Inyo Mountains. They occur in narrow belts and blocks rather than continuous statewide coverage.
• Precambrian metasedimentary rocks. These rocks are also shown in eastern California, commonly associated with the same regions where Precambrian metamorphic rocks are mapped. They appear in elongate outcrop areas within mountain ranges east of the Sierra Nevada.

The figure place the Precambrian rocks in the context of California’s overall geologic framework. 

• Cenozoic (0–65 Ma)
  • Cenozoic nonmarine (continental) sedimentary rocks and alluvial deposits (~0.011–65 Ma). These rocks are shown mainly in large lowland areas, especially the Central Valley and other broad interior basins. They also appear in smaller patches along major river valleys and coastal lowlands.
  • Cenozoic marine sedimentary rocks (~1.6–65 Ma). These rocks occur primarily along the coastal regions of California. They form discontinuous belts near the shoreline and adjacent offshore-margin areas.
  • Cenozoic volcanic rocks (~1.6–65 Ma). These rocks are concentrated in northeastern California and parts of eastern California. Smaller volcanic areas also appear scattered in the Coast Ranges and southern California.
• Mezozoic (65–245 Ma)
  • Late Mesozoic (latest Jurassic and Cretaceous) marine sedimentary rocks; Great Valley Sequence and related rocks (~145–65 Ma). These rocks form a long, continuous band along the western side of the Central Valley. They are positioned between the Coast Ranges and the Sierra Nevada.
  • Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed (~245–65 Ma). These rocks occur mainly in the Sierra Nevada foothills and parts of the Klamath Mountains. They appear as elongated belts adjacent to large areas of granitic rocks.
  • Late Mesozoic (latest Jurassic and Cretaceous) Franciscan Complex (~145–65 Ma). This unit is widely distributed throughout the Coast Ranges of California. It forms a broad, irregular belt parallel to the coastline.
  • Granitic rocks chiefly Mesozoic (~245–65 Ma). These rocks dominate the Sierra Nevada and form a large, continuous region there. Smaller granitic bodies also appear in southern California and parts of the Coast Ranges.
  • Serpentinized ultramafic rocks chiefly Mesozoic (~245–65 Ma). These rocks occur as narrow, scattered bodies primarily within the Coast Ranges and the Klamath Mountains. They are also present in small patches along major fault zones.
• Paleozoic (245–570 Ma)
  • Paleozoic sedimentary and volcanic rocks; in places strongly metamorphosed (~570–245 Ma). These rocks are found in eastern California and in parts of the Klamath Mountains. They also appear in smaller, isolated areas within mountain ranges.
• Pre-Cenozoic (>65 Ma)
  • Pre-Cenozoic metamorphic rocks of unknown age (>65 Ma). These rocks are shown in scattered areas within mountain belts across the state. They commonly occur adjacent to granitic rocks in the Sierra Nevada and southern California.

Figure 6.2.6 Rifting of a Continental Plate

This diagram illustrates how a continental landmass begins to split apart and eventually forms new oceanic crust. The figure shows stretching and thinning of the continental lithosphere, which leads to the development of deep basins and the upwelling of hot mantle material from below. As rifting progresses, surface rocks fracture along large normal faults, and the crust becomes increasingly thin. Continued extension allows molten rock to rise and form new basaltic crust in the center of the rift. This process marks the transition from a continent-breaking-apart environment to the formation of a young ocean basin. The diagram represents the early stages of what would eventually become the passive margin along the ancient western edge of North America.

Figure 6.3.1 Thrust System and Allochthonous Rocks

This figure depicts a simplified model of a thrust fault system in which older rocks are pushed above younger rocks due to compressional forces. The upper block of rock, which has been transported from elsewhere, is called an allochthon. It rests above the lower block, known as the autochthon, which remains in its original position. This type of deformation results from horizontal compression associated with convergent plate boundaries.

The figure also includes a klippe: an isolated remnant of the thrust sheet (the allochthon) that has been left behind after erosion removes most of the surrounding overlying rock. Also included is a window which occurs erosion cuts through the overlying thrust sheet, creating an opening that exposes the underlying autochthonous rocks beneath. 

Figure 6.3.2 Western Pacific as an Analog for Paleozoic Tectonics

This is a map of the modern western Pacific region that is used as an analogy for the Paleozoic tectonic environment of western North America. It includes multiple subduction zones, volcanic island arcs, ocean basins, and microcontinents. The purpose of the figure is to show that during the Paleozoic, the margin of Laurentia was not a simple passive margin but included oceanic plates and island arcs separated by narrow basins, much like the western Pacific today. The image emphasizes that material from different tectonic environments can later become accreted to a continental margin as convergence continues.

Locations of each tectonic plate boundary:

• Continental / oceanic convergent boundary. This boundary type appears along the margins of island chains and continental edges. It is found near labeled locations such as the Aleutian Arc, Kuril Arc, Japan Arc, Ryukyu Arc, Izu-Bonin Arc, and Mariana Arc, and along boundaries adjacent to the Philippines and New Hebrides – Fiji regions. 
• Continental rift boundary / oceanic spreading ridge. This boundary type appears in open ocean areas where boundary lines pass through water between landmasses. It is found in regions labeled Banda Sea, Woodlark, Manus, and near South Bismarck and North Bismarck.
• Continental / oceanic transform fault. This boundary type appears as straight or gently curving boundary segments that run alongside other boundaries. It is found near labeled regions such as Timor, Birds Head, Solomon Sea, and along boundary segments near New Guinea and surrounding islands.
• Non-subducting plate boundaries (type not specified). These boundaries appear as simple boundary lines without additional symbols. They are found between labeled regions such as Caroline, Manus, North Bismarck, and South Bismarck, and in several ocean areas without trench labels.
• Subduction zone. This boundary type appears as curved boundary lines adjacent to trench labels. It is found at locations labeled Marianas Trench, Philippines Trench, Tonga Trench, and along curved boundaries near Sumatra, Timor, and New Hebrides – Fiji.

The map uses arrows with numbers to show plate velocities relative to Africa. Africa is the reference frame, so other plates have arrows indicating both direction of motion and speed compared to Africa.

• The Pacific Plate has long arrows pointing generally westward or northwestward, with larger numerical values, indicating faster motion relative to Africa.
• Plates closer to Africa, such as the Eurasian Plate and Indian Plate, have shorter arrows with smaller numbers, indicating slower motion relative to Africa.
• Southern plates such as the Australian Plate and Antarctic Plate have arrows pointing generally northward or northeastward, each labeled with a specific cm/yr value.
• Plates in the Americas, such as the North American Plate, show arrows pointing generally westward, with moderate numerical values.

Figure 6.3.3 Truncated Passive Margin by the California-Coahuila Transform

This figure illustrates how part of the Paleozoic passive margin and its sedimentary deposits were displaced along a large-scale transform fault known as the California–Coahuila transform. The diagram shows that a block of continental crust referred to as the Caborca Block was shifted relative to the remainder of the margin. This motion displaced the original alignment of shelf sediments and accreted terranes, explaining why these rocks are not continuous across the present-day region.

Figure 6.4.1 Distribution of Mesozoic Granitoids in California

This map highlights the areas in California underlain by large bodies of granitoid rock that formed during Mesozoic subduction (~245–65 Ma). The plutonic rocks, which cooled slowly from magma deep within the crust, form the core of mountain ranges such as the Sierra Nevada and the Peninsular Ranges. The spatial pattern of these rocks outlines the location of a former magmatic arc generated above a subduction zone. The figure provides evidence that subduction-related magmatism was widespread and long-lasting during the Mesozoic.

The figure place the Precambrian rocks in the context of California’s overall geologic framework. 

• Cenozoic (0–65 Ma)
  • Cenozoic nonmarine (continental) sedimentary rocks and alluvial deposits (~0.011–65 Ma). These rocks are shown mainly in large lowland areas, especially the Central Valley and other broad interior basins. They also appear in smaller patches along major river valleys and coastal lowlands.
  • Cenozoic marine sedimentary rocks (~1.6–65 Ma). These rocks occur primarily along the coastal regions of California. They form discontinuous belts near the shoreline and adjacent offshore-margin areas.
  • Cenozoic volcanic rocks (~1.6–65 Ma). These rocks are concentrated in northeastern California and parts of eastern California. Smaller volcanic areas also appear scattered in the Coast Ranges and southern California.
• Mezozoic (65–245 Ma)
  • Late Mesozoic (latest Jurassic and Cretaceous) marine sedimentary rocks; Great Valley Sequence and related rocks (~145–65 Ma). These rocks form a long, continuous band along the western side of the Central Valley. They are positioned between the Coast Ranges and the Sierra Nevada.
  • Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed (~245–65 Ma). These rocks occur mainly in the Sierra Nevada foothills and parts of the Klamath Mountains. They appear as elongated belts adjacent to large areas of granitic rocks.
  • Late Mesozoic (latest Jurassic and Cretaceous) Franciscan Complex (~145–65 Ma). This unit is widely distributed throughout the Coast Ranges of California. It forms a broad, irregular belt parallel to the coastline.
  • Serpentinized ultramafic rocks chiefly Mesozoic (~245–65 Ma). These rocks occur as narrow, scattered bodies primarily within the Coast Ranges and the Klamath Mountains. They are also present in small patches along major fault zones.
• Paleozoic (245–570 Ma)
  • Paleozoic sedimentary and volcanic rocks; in places strongly metamorphosed (~570–245 Ma). These rocks are found in eastern California and in parts of the Klamath Mountains. They also appear in smaller, isolated areas within mountain ranges.
• Precambrian (older than 570 Ma)
  • Precambrian rocks of all types including coarse-grained intrusives (>570 Ma). These rocks are restricted mainly to southeastern California. They appear as isolated patches within desert mountain ranges.
• Pre-Cenozoic (>65 Ma)
  • Pre-Cenozoic metamorphic rocks of unknown age (>65 Ma). These rocks are shown in scattered areas within mountain belts across the state. They commonly occur adjacent to granitic rocks in the Sierra Nevada and southern California.

Figure 6.4.2 Distribution of Mesozoic Franciscan Complex

This map shows the geographic extent of the Franciscan Complex along the California Coast Ranges. The Franciscan Complex (~145–65 Ma) is composed of highly deformed sedimentary and volcanic rocks that were scraped off the downgoing oceanic plate in a subduction zone. These rocks were transported to great depth, metamorphosed under high pressure, and then returned to the surface. The irregular distribution of rock types reflects the chaotic nature of subduction and accretion processes.

The figure place the Precambrian rocks in the context of California’s overall geologic framework. 

• Cenozoic (0–65 Ma)
  • Cenozoic nonmarine (continental) sedimentary rocks and alluvial deposits (~0.011–65 Ma). These rocks are shown mainly in large lowland areas, especially the Central Valley and other broad interior basins. They also appear in smaller patches along major river valleys and coastal lowlands.
  • Cenozoic marine sedimentary rocks (~1.6–65 Ma). These rocks occur primarily along the coastal regions of California. They form discontinuous belts near the shoreline and adjacent offshore-margin areas.
  • Cenozoic volcanic rocks (~1.6–65 Ma). These rocks are concentrated in northeastern California and parts of eastern California. Smaller volcanic areas also appear scattered in the Coast Ranges and southern California.
• Mezozoic (65–245 Ma)
  • Late Mesozoic (latest Jurassic and Cretaceous) marine sedimentary rocks; Great Valley Sequence and related rocks (~145–65 Ma). These rocks form a long, continuous band along the western side of the Central Valley. They are positioned between the Coast Ranges and the Sierra Nevada.
  • Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed (~245–65 Ma). These rocks occur mainly in the Sierra Nevada foothills and parts of the Klamath Mountains. They appear as elongated belts adjacent to large areas of granitic rocks.
  • Granitic rocks chiefly Mesozoic (~245–65 Ma). These rocks dominate the Sierra Nevada and form a large, continuous region there. Smaller granitic bodies also appear in southern California and parts of the Coast Ranges.
  • Serpentinized ultramafic rocks chiefly Mesozoic (~245–65 Ma). These rocks occur as narrow, scattered bodies primarily within the Coast Ranges and the Klamath Mountains. They are also present in small patches along major fault zones.
• Paleozoic (245–570 Ma)
  • Paleozoic sedimentary and volcanic rocks; in places strongly metamorphosed (~570–245 Ma). These rocks are found in eastern California and in parts of the Klamath Mountains. They also appear in smaller, isolated areas within mountain ranges.
• Precambrian (older than 570 Ma)
  • Precambrian rocks of all types including coarse-grained intrusives (>570 Ma). These rocks are restricted mainly to southeastern California. They appear as isolated patches within desert mountain ranges.
• Pre-Cenozoic (>65 Ma)
  • Pre-Cenozoic metamorphic rocks of unknown age (>65 Ma). These rocks are shown in scattered areas within mountain belts across the state. They commonly occur adjacent to granitic rocks in the Sierra Nevada and southern California.

Figure 6.4.3 Distribution of Mesozoic Great Valley Group Sedimentary Rocks

This map illustrates the location of sedimentary rocks of the Great Valley Group, which formed in a forearc basin between the Mesozoic volcanic arc and the subduction zone (~145–65 Ma). These rocks accumulated as thick layers of sand and mud transported by rivers draining the rising Sierra Nevada. The sediments formed deep marine submarine fan systems that filled the basin. The distribution of these rocks records the position of the forearc basin and helps reconstruct the geometry of the late Mesozoic continental margin.

The figure place the Precambrian rocks in the context of California’s overall geologic framework. 

• Cenozoic (0–65 Ma)
  • Cenozoic nonmarine (continental) sedimentary rocks and alluvial deposits (~0.011–65 Ma). These rocks are shown mainly in large lowland areas, especially the Central Valley and other broad interior basins. They also appear in smaller patches along major river valleys and coastal lowlands.
  • Cenozoic marine sedimentary rocks (~1.6–65 Ma). These rocks occur primarily along the coastal regions of California. They form discontinuous belts near the shoreline and adjacent offshore-margin areas.
  • Cenozoic volcanic rocks (~1.6–65 Ma). These rocks are concentrated in northeastern California and parts of eastern California. Smaller volcanic areas also appear scattered in the Coast Ranges and southern California.
• Mezozoic (65–245 Ma)
  • Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed (~245–65 Ma). These rocks occur mainly in the Sierra Nevada foothills and parts of the Klamath Mountains. They appear as elongated belts adjacent to large areas of granitic rocks.
  • Late Mesozoic (latest Jurassic and Cretaceous) Franciscan Complex (~145–65 Ma). This unit is widely distributed throughout the Coast Ranges of California. It forms a broad, irregular belt parallel to the coastline.
  • Granitic rocks chiefly Mesozoic (~245–65 Ma). These rocks dominate the Sierra Nevada and form a large, continuous region there. Smaller granitic bodies also appear in southern California and parts of the Coast Ranges.
  • Serpentinized ultramafic rocks chiefly Mesozoic (~245–65 Ma). These rocks occur as narrow, scattered bodies primarily within the Coast Ranges and the Klamath Mountains. They are also present in small patches along major fault zones.
• Paleozoic (245–570 Ma)
  • Paleozoic sedimentary and volcanic rocks; in places strongly metamorphosed (~570–245 Ma). These rocks are found in eastern California and in parts of the Klamath Mountains. They also appear in smaller, isolated areas within mountain ranges.
• Precambrian (older than 570 Ma)
  • Precambrian rocks of all types including coarse-grained intrusives (>570 Ma). These rocks are restricted mainly to southeastern California. They appear as isolated patches within desert mountain ranges.
• Pre-Cenozoic (>65 Ma)
  • Pre-Cenozoic metamorphic rocks of unknown age (>65 Ma). These rocks are shown in scattered areas within mountain belts across the state. They commonly occur adjacent to granitic rocks in the Sierra Nevada and southern California.

Figure 6.4.4 Sevier Orogeny Cross Section

This is a cross-sectional diagram illustrating the tectonic processes during the Sevier Orogeny, which was a mountain-building event that affected western North America during the Late Cretaceous. The diagram presents a simplified west-to-east slice through the region, showing the geological features and tectonic interactions at the time.

On the left (west) side of the diagram, the Sierra Nevada mountain range is depicted, with an active volcano shown. A magma reservoir is shown within the crust, but the volcano shaft extends down through the lithospheric mantel and the asthenosphere to the Farallon Plate, which is subducting beneath the North American Plate at a steep angle.

Beneath the North American Plate lies the lithospheric mantle, and below that is the asthenosphere, a layer of the Earth's mantle that is involved in the tectonic movement. The angle of the subducting Farallon Plate becomes becoming less steep as it subducts. This is indicated on the diagram as the shallowing plate.

Moving to the right (east) side, the diagram shows the overthrust belt, where rock layers have been pushed over one another due to compression, which is a key feature of the Sevier Orogeny. The Western Interior Seaway is a body of water extending to the east of the mountain range.

Figure 6.4.5 Paleogeographic Maps

During the Sevier Orogeny, at ~75 Ma, much of North America was submerged. Most of modern-day Mexico was under water, with only a strip of land along its western flank visible. Much of what is now Texas, Louisiana, North and South Carolina, Florida, and coastal states along the Eastern Seaboard were submerged. An inland sea is shown in a rough Y shape. The western leg is shown extending from what is now the Yukon and Alberta in Canada through a swath including what is now Montana, Wyoming, and Colorado to empty into the sea in what is now eastern Texas; the eastern leg splits off (approximately) where Minnesota is now and extends northeast through Quebec, Canada, where it meets the wider ocean.

By the time of the Laramide Orogeny, at ~65 Ma, most of the inland sea has disappeared and the North American coastline is closer to what we would recognize today. Much of the area that is now Mexico has uplifted, as has much of Texas and the gulf states (although the Texas panhandle is still submerged). A remnant of the inland sea remains as a curved arc entering along what is now eastern Texas and moving up through modern-day Oklahoma, Colorado, Wyoming, and South Dakota.

Figure 6.4.6 Laramide Orogeny Cross Section

This image is a cross-sectional diagram depicting the tectonic setting during the Laramide Orogeny, showing a west-to-east slice through the western United States. On the west side, the Sierra Nevada mountain range a relatively low, rounded highland. Beneath it, the Farallon Plate is a broad, gently dipping slab moving eastward beneath the North American continent. Toward the east, the Rocky Mountains a series of high, rugged peaks. The crust beneath them rests above the lithospheric mantle.

The Farallon Plate extends beneath the entire section, subducting at a shallow angle beneath the North American Plate, and descending at a much lower angle than typical subduction zones.

Figure 6.4.7 Features Associated with the Laramide Orogeny

The Laramide Orogeny was a mountain-building event that affected western North America during the Late Cretaceous to early Paleogene.

The main portion of the image is a simplified map of the western United States, showing major structural features of the Laramide and Sevier Orogenies. The Sevier fold and thrust belt is depicted as a series of parallel, wavy lines running from the southwestern U.S. toward the northwest. To the east of the Sevier belt, the Laramide uplifts are marked, representing block uplifts of Precambrian basement rock that formed during the Laramide Orogeny.

Glacier National Park is labeled near the northernmost extent of the Sevier fold and thrust belt. The Pacific Ocean is labeled to indicate the western boundary of the region.

Two cross-sectional diagrams on the right illustrate the geological processes occurring during and after the Laramide Orogeny.

During Laramide Mountain-Building

• This diagram represents an uplifted region during the Laramide Orogeny.
• A deep-seated fault cuts through the Precambrian basement complex, forcing it upward and tilting overlying Paleozoic and Mesozoic sedimentary layers.
• The faulting causes the formation of a Laramide uplift (a block of rock pushed upward) adjacent to a down-dropped basin.

Post-Erosion and Deposition

• This diagram shows the landscape after erosion and sediment deposition.
• The uplifted block remains structurally elevated but has been subjected to erosion, reducing its topographic relief.
• In the adjacent down-dropped basin, younger Cenozoic strata have accumulated, burying parts of the faulted sedimentary layers.

Figure 6.5.1 Tectonic Evolution of the West Coast Plate Boundary: 30 Million Years Ago to Present

This four-panel image illustrates the tectonic evolution of the Pacific–North American plate boundary over time, from 30 million years ago to the present. It shows how the subduction of the Farallon Plate has been replaced by a transform boundary (the San Andreas Fault Zone) as new plates formed and spreading centers shifted. 

30 Million Years Ago

• The Farallon Plate is subducting beneath the North American Plate at a long, continuous trench.
• The Pacific Plate is to the west of the Farallon Plate.
• A spreading center (divergent boundary) is shown along the southeast edge of the Pacific Plate.
• The San Andreas Fault has not yet formed.

20 Million Years Ago

• Two sections of the Pacific Plate come into view. The southmost section begins to subduct beneath the North American Plate in roughly the area where Los Angeles is located today. As it moves, it bisects the Farallon Plate, which becomes the Juan de Fuca Plate in the north and Cocos Plate in the south.
• Long trenches remain where the North American Plate abuts the Juan De Fuca and Cocos plates.
• Spreading centers (divergent boundaries) are shown along the southeast edges of the Pacific Plate where it meets the Juan De Fuca Plate in the north and the Cocos Plate in the south.
• Triple junctions are indicated where the Pacific Plate meets the North American Plate:
  • In the north, the Mendocino Triple Junction is where the Juan De Fuca, Pacific, and North American plates meet.
  • In the south, the Rivera Triple Junction is where the Cocos, Pacific, and North American plates meet.
  • A transform fault (early San Andreas Fault) has begun forming between the Pacific and North American plates, as the Pacific Plate moves in a northward direction and the North American Plate moves southward.

10 Million Years Ago

• As the Pacific Plate (moving northward) continues to subduct beneath the North American Plate (moving southward), the transform fault becomes longer. It stretches from roughly what is now Central California in the north to what is now Baja California in the south; accordingly, the distance between the Mendocino and Rivera triple junctions has increased dramatically.
• Trenches remain where the North American Plate abuts the Juan De Fuca and Cocos plates.
• Spreading centers (divergent boundaries) are shown along the southeast edges of the Pacific Plate where it meets the Juan De Fuca Plate in the north and the Cocos Plate in the south.

Present

• As the Pacific Plate slides northwest past the North American Plate, the San Andreas Fault is a dominant boundary feature. It now extends from the Mendocino Triple Junction north of San Francisco to the Rivera Triple Junction in the Gulf of California.
• The Juan de Fuca Plate is shown in the north, bordered by a trench along its south edge where it meets the North American Plate.
• The Rivera Plate now appears along the coast of Mexico, bounded on the east by the trench along the North American Plate. It is shown as a rough triangle with the Rivera Triple Junction as one of its points.
• The Cocos Plate still appears in the south, at the bottom of the map, bounded on the east by the trench along the North American Plate.
• Spreading centers (divergent boundaries) are still shown along the southeast edges of the Pacific Plate where it meets the Juan De Fuca Plate in the north, and where it meets the Rivera and Cocos plates in the south. However, additional divergent boundaries now appear along the San Andreas Fault from roughly its midpoint and moving south.