The Salton Basin is a land of physical extremes. The tallest mountain peaks in Southern California lay to the north — Mt. San Gorgonio (11,502 feet) and Mt. San Jacinto (10,804 feet), with cool temperatures, ample rainfall, and alpine vegetation. Winter persists on the higher peaks for eight months out of the year, with snow accumulations of over 60 feet on some slopes of Mt. San Gorgonio. Yet just 50 miles to the south lies the Salton Sea at -227 feet below sea level.

Some introductory information on the science of the Salton Sea area follows. For more detailed information and many helpful illustrations, see the online Salton Sea Atlas.

Geology

Hot molten magma from deep within the earth rises to the surface along a narrow fracture that runs the length of the East Pacific. The new lava pushes older material away from the spreading zone, forming the East Pacific Rise. Where cooler, dense ocean crust crashes against lighter continental material, the heavier oceanic crust is pushed beneath (subducted) the continents, forcing the ocean crust back into the furnace of the earth. Some of this material melts and bubbles back up to the surface, forming the chains of volcanoes that comprise the Andes and the Central American volcanic cordillera.

Hydrology

The Lower Colorado River has changed its course many times in the past. Before being cut off by the current extent of the delta, the Salton Basin was part of the Gulf of California, reaching as far north as present day Indio. Sedimentary deposits borne of the torrential flows that cut the Grand Canyon established a massive natrual dam, or berm, across the Gulf, isolating the basin. The isolated lake soon evaporated in the arid desert climate, leaving a barren depression below sea level — the Salton Basin. The Gulf was pushed further and further to the south as the buildup of sediments continued.

In the several million years that followed, the Lower Colorado River has changed course many times, driven by periodic floods and blocked by sedimentary fill deposits, sometimes flowing south directly to the Gulf, and sometimes to the north, filling the Salton Basin to its brim, before spilling back to the Gulf over the drainage divide, located about 15 mile south of Mexicali. The periodic infillings of the basin, collectively called Lake Cahuilla, averaged about 18 years to fill each time, creating a lake over 300 feet deep and covering approximately three times the surface area of hte current Salton Sea. Today, agricultural runoff fed by the Colorado River is what largely maintains the Sea.

Limnology

The Salton Sea has been sustained by nutrient rich inflows for the past 100 years. Since the Sea has no outflow, water leaves the Sea mainly through evaporation, leaving behind salts, minerals, and other substances — millions of tons over the past century. This accumulation of substances creates an ever-changing chemistry. As oxygen solubility decreases, many chemical processes change. Previously oxidized compounds may be altered, dissolving or resting in bottom sediment.

Nutrients, such as nitrogen and phosphorus, are essential for life. Oversupply of certain nutrients stress lake ecology and change the chemistry. High levels of nitrogen, under certain conditions, form ammonia gas, which can be toxic. In the Sea, excess nitrogen, along with other factors, such as high temperatures and low dissolved oxygen, contribute to environmental stress in aquatic life, causing periodic population crashes.

Biology

The Salton Basin comprises one of the most diverse collections of plants and animals in North America, principally due to its extreme topography and climates. From searing tropical desert bajadas (shallow slopes at the base of rocky hills) to icy alpine summits, habitats change dramatically in very short distances. As elevation increases, the cooler temperatures support different species. These steep slopes support remarkably diverse plant and animal communities — adjacent habitats, yet so distinct from one another they are termed "life zones."