12.6: Chapter Summary

12.1 Physiographic Properties and Characteristics of the Great Valley

• The Great Valley in California is a large, flat region that stretches over 644 kilometers (400 miles) with a width of 80 kilometers (50 miles). It is divided into the Sacramento Valley in the north and the San Joaquin Valley in the south.
• The Great Valley is a geographically diverse region with distinct parts, the Sacramento Valley and the San Joaquin Valley, known for its agricultural productivity.
• The San Joaquin Valley is a Mediterranean environment with hot, dry summers and wet winters. It is a major agricultural region, producing a significant portion of the United States' agricultural products, including grapes, raisins, cotton, almonds, citrus, and vegetables.
• The San Joaquin Valley plays a significant role in supplying a wide range of agricultural products for the United States.
• The Great Valley is filled with sediment deposits that are several kilometers deep, with the San Joaquin Valley reaching up to 4.8 kilometers (3 miles) and the Sacramento Valley up to 9.6 kilometers (6 miles). Groundwater pumping for agriculture has caused subsidence, particularly in areas with fine-grained sediments.
• Groundwater pumping for agriculture has led to subsidence in certain areas of the Great Valley, highlighting the importance of sustainable water management practices.

12.2 Geology of the Great Valley

• The Great Valley is a sedimentary basin with a thick sequence of sedimentary units called the Great Valley Sequence. It was formed through tectonic activities and the Western Interior Seaway, which covered much of California with ocean water.
• The Great Valley, including the Sacramento Valley and the San Joaquin Valley, has a diverse and dynamic geologic history influenced by tectonic forces, sedimentation, and climate changes.
• The Sacramento Valley in Northern California has a complex geologic history shaped by tectonic activities, including subduction, uplift of the Sierra Nevada Mountains, and the creation of the California Coast Ranges.
• The formation of the valley involved a series of events ranging from ancient oceans, tectonic uplift, and deposition of sediment from nearby mountains and key fluvial systems such as the Sacramento and Feather Rivers.
• The San Joaquin Valley in central California has a rich geologic history influenced by tectonic activity, sedimentation, and erosion. The region has been shaped by the movement along the San Andreas Fault and the deposition of sediment from granitic blocks, contributing to the formation of turbidite deposits and petroleum reserves.
• The formation of the valley involved a series of events ranging from ancient oceans, tectonic uplift, and deposition of sediment from nearby mountains, with dominant influence from the San Andreas Fault system to the west and fluvial systems to the east.

12.3 Soil, Streams and Agriculture

• The Great Valley's surface is predominantly covered by recent and Pleistocene-age alluvium, deposited by streams carrying sediment from the Sierra Nevada and nearby ranges. The clay-rich sediments contribute to the fertility of the agricultural land and are periodically replenished by spring runoff.
• The Great Valley's fertile agricultural land is primarily composed of clay-rich alluvium deposited by streams originating from the Sierra Nevada and nearby ranges.
• Periodic glaciation of the Sierra Nevada has resulted in the accumulation of sediment in moraines, which rivers transported downstream during wetter climate periods. These episodic alluvial deposits, known as glacial outwash, have contributed to the sedimentation in the Great Valley over the past 2 million years.
• Glacial outwash from the Sierra Nevada during periods of glaciation has significantly influenced the sedimentation in the Great Valley.
• In the central to lower parts of the Great Valley, younger alluvium has buried older sediment deposits. However, along the Sierra foothills, older alluvium can still be observed at the surface. Ongoing uplift of the Sierra Nevada has led to river downcutting and the formation of stream terraces, providing a record of the valley's sequential geological history.
• Ongoing uplift of the Sierra Nevada has resulted in river downcutting and the formation of stream terraces, revealing the valley's geological history and the burial of older sediment layers.

12.4 Natural Hazards

• The Great Valley of California faces a range of natural hazards, including seismic activity, flooding, drought, and wildfires. These hazards demand careful planning and preparedness to mitigate risks and protect residents and infrastructure.
• The Great Valley faces a diverse range of natural hazards, including earthquakes, floods, droughts, and wildfires, which require proactive planning and response measures.
• Land subsidence is a significant problem in the Great Valley, primarily caused by extensive groundwater extraction for agriculture. This sinking of the land has detrimental effects on infrastructure, increases flood risk, and poses challenges to water management.
• Land subsidence caused by excessive groundwater extraction poses risks to infrastructure and water management.
• The Great Valley is susceptible to seismic hazards, primarily from nearby faults such as the Sierra Nevada frontal fault system and the Concord-Green Valley Fault. While the Great Valley itself is relatively seismically stable, the transmission of earthquakes from surrounding fault systems can pose risks.
• Understanding the seismic hazards from nearby faults and their potential impacts is crucial for ensuring the safety and resilience of the Great Valley's communities.
• The Great Valley in California, stretching from the Sacramento Valley to the San Joaquin Valley, is susceptible to significant flooding due to its low-lying nature and the presence of major rivers like the Sacramento and San Joaquin. Heavy rainfall, snowmelt, and inadequate drainage systems can lead to overflowing rivers, breached levees, and widespread inundation.
• The Great Valley in California faces a significant flood hazard due to its geographical characteristics, major rivers, and inadequate drainage systems.
• The flat and fertile nature of the valley, along with an extensive irrigation network, contribute to the challenge of excess water removal during intense rainfall or river surges.
• The Tulare Lake Basin experiences a complex relationship between water availability, agriculture, and climate change, highlighting the need for sustainable water management practices in the region.

12.5 Natural Resources of the Great Valley

• The Great Valley in California is rich in natural resources, including oil and natural gas, groundwater, and mineral deposits such as metallic ores. These resources play a significant role in the region's energy production, agricultural activities, and industrial development.
• The Great Valley's natural resources, such as oil and natural gas, groundwater, and mineral deposits, are essential for energy production, agricultural productivity, industrial growth, and economic development.
• Petroleum extraction is a vital industry in the Great Valley, with substantial reserves of oil and natural gas found in the underground sedimentary formations. The geological process of petroleum formation, migration, and trapping contributes to the presence of these valuable fossil fuels.
• The same key concepts used in petroleum reservoir identification are being used today to identify subsurface carbon capture and sequestration project potential.
• Groundwater is a crucial resource in the Great Valley, supporting agricultural irrigation, industrial activities, and domestic water supply. The availability and accessibility of groundwater sustain the region's extensive agricultural sector and promote economic growth.
• Proper management and sustainable use of these resources are crucial for ensuring long-term economic viability and environmental stewardship in the region.
• The Great Valley is known for its diverse mineral resources, including metallic ores and minerals used in construction and industry. Copper, gold, silver, and other metals are extracted from the region's mines and play a vital role in various industries.
• The geological characteristics and processes that have created these resources highlight the importance of understanding and protecting the Great Valley's geology for future generations.