8.3: Modoc Plateau
The Modoc Plateau is in the northeastern corner of the state, framed by and including the Warner Mountains and Surprise Valley along the Nevada border to the east and west to the edge of the southern Cascades Range. The area extends north to the Oregon border and south to include the Skedaddle Mountains and the Honey Lake Basin. While there have been volcanoes and lava flows in nearly all parts of California at various times in its geologic past, it is in the northeastern portion that we find the most extensive. One of the greatest lava floods of Earth's surface covers Eastern Oregon, Eastern Washington, Southern Idaho, Northern Nevada, and Northeastern California.
Physical Geography
The Modoc Plateau Province encompasses over 7 million acres in the far northeastern corner of California. This province is composed of two distinct geographic and ecological areas, the Modoc Plateau, and the Southern Cascades. Elevations in the province average higher than other provinces, ranging from 3,000 feet throughout the Modoc Plateau to over 14,000 feet on mountain peaks of the Southern Cascades. Northeastern California is an outstanding region for wildlife, providing habitat for mountain lion, black-tailed deer, mule deer, pronghorn, elk, yellow-bellied marmot, porcupine, greater sage-grouse, and the colorful waterfowl of the Pacific Flyway that funnel through the area during their annual migrations. Golden eagle, prairie falcon, cascade frog, southern long-toed salamander, Northern goshawk, Northern spotted owl, sooty grouse, greater sandhill crane, and American white pelican nest and hunt or forage in varied habitats in the province. Sharp-tailed grouse historically occurred in this province but have been extirpated. The varied aquatic habitats and natural barriers along the Pit River and Klamath River and their tributaries have allowed the evolution of several unique aquatic communities that include endemic fish and invertebrates in the Cascades and Modoc Plateau Province.
Physical Geology
A million years ago, layered lava flows formed the 4,000–5,000-foot elevation Modoc Plateau, separating the watersheds of the area from the Klamath drainage to the northwest. The waters of the western slope of the Warner Mountains and the Modoc Plateau carved a new course, the Pit River, flowing to the southwest through the Cascades and joining the Sacramento River at Lake Shasta. Many of the springs and creeks of northeastern California drain via the Pit River.
Situated on the western edge of the Great Basin, the Modoc Plateau has supported high desert plant communities and ecosystems like that region—shrub-steppe, perennial grasslands, sagebrush, antelope bitterbrush, mountain mahogany, and juniper woodlands. Sagebrush plant communities are characteristic of the area, providing important habitat for sagebrush-dependent wildlife such as greater sage-grouse and pygmy rabbit. Conifer forests dominate the higher elevations of the Warner Mountains and the smaller volcanic mountain ranges and hills that shape the area. Wetland, spring, meadow, vernal pool, riparian, and aspen communities scattered across the rugged and otherwise dry desert landscape support diverse wildlife. The area has varied aquatic habitats, from high mountain streams to the alkaline waters of Goose Lake and Eagle Lake to clear spring waters of Fall River and Ash Creek.
Case Study - Lava Beds National Monument
One of the most iconic geologic areas found within the plateau is the Lava Beds National Monument, which is geologically significant because of its wide variety of volcanic formations, including lava tubes, fumaroles, cinder cones, spatter cones, pit craters, hornitos, maars, lava flows, and volcanic fields.
Cinder cones are formed when magma is under great pressure. It is released in a fountain of lava, blown into the air from a central vent. The lava cools as it falls, forming cinders that pile up around the vent. When the pressure has been relieved, the rest of the lava flows from the base of the cone. Cinder cones are typically monogenetic, meaning that they are a volcano that erupts only once. These volcanoes are typically smaller and less complex than volcanoes that erupt repeatedly (polygenetic volcanoes).
The cinder cones of Hippo Butte, Three Sisters, Juniper Butte, and Crescent Butte are all older than the Mammoth and Modoc Crater flows, more than 30,000–40,000 years old. Eagle Nest Butte and Bearpaw Butte are 114,000 years old. Schonchin Butte cinder cone, figure 8.9) and the andesitic flow from its base were formed around 62,000 years ago. The flow that formed Valentine Cave erupted 10,850 years ago. An eruption that formed The Castles is younger than the Mammoth Crater flows. Even younger were eruptions from Fleener Chimneys, such as the Devil's Homestead flow, 10,500 years ago, and Black Crater 3,025 years ago. About 1,110 years ago, plus or minus 60 years, the Callahan flow was produced by an eruption from Cinder Butte. Though Cinder Butte is just outside the boundary of the monument, the Callahan flow is in Lava Beds and is the youngest flow in the monument.
Spatter cones are built out of thicker lava. The lava is thrown out of the vent and builds, layer by layer, a chimney surrounding the vent. Fleener Chimneys and Black Crater are examples of spatter cones.
Roughly ninety percent of the lava in the Lava Beds Monument is basaltic. There are primarily two kinds of basaltic lava flows: pahoehoe and ʻaʻā. Pahoehoe is smooth, often ropy and is the most common type of lava in Lava Beds. ʻAʻā is formed when pahoehoe cools and loses some of its gases. ʻAʻā is rough, sharp, and jagged; an excellent example is the Devil's Homestead lava flow, which originated at Fleener Chimneys. Most of the rest of the lava in the monument is andesitic. Pumice, a rapidly cooled type of volcanic glass, also is found covering the monument; this rained down around 900 years ago during the eruption of Glass Mountain.
The flows from Mammoth and Modoc Craters comprise about two-thirds of the lava in the monument. Over 30 separate lava flows located in the park range in age from 2,000,000 years to 1,110 years years ago. Some of the major lava flows within Lava Beds National Monument include the Callahan Flow; Schonchin Flow; Mammoth Crater Flow; Modoc Crater Flow; and Devil's Homestead Flow (figure 8.11).
Lava Beds National Monument has the largest concentration of lava tubes in North America. Lava flows dated to about 30,000–40,000 years ago formed most of the lava tubes in the monument. As the hot basaltic lava flowed downhill, the top cooled and crusted over, insulating the rest of the lava, and forming lava tubes. Lavacicles on the ceiling of a lava tube were produced as the level of lava in the tube retreated and the viscous lava on the ceiling dripped as it cooled.
Cultural Geography - Case Study – The Modoc
The Modoc are an Indigenous American people who historically lived in the area which is now northeastern California and central Southern Oregon. Currently, they include two federally recognized tribes, the Klamath Tribes in Oregon, and the Modoc Tribe of Oklahoma, now known as the Modoc Nation. The Modoc, like the neighboring Klamath, spoke dialectic varieties of the Klamathan/Lutuamian language, a branch of the Plateau Penutian language family. Both peoples called themselves maklaks , meaning "people". To distinguish between the tribes, the Modoc called themselves Moatokni maklaks, from muat meaning "South". The Achomawi, a band of the Pit River tribe, called them Lutuami , meaning "Lake Dwellers".