Bordered on the east by the high Sierra Nevada and separated from the Pacific Ocean by the Coast Range mountains, the San Joaquin Valley is 250 miles long and 50 miles wide, and the flat, open landscape includes parts of eight counties.
The San Joaquin River, the Valley’s namesake, runs the length of the region north from the Tulare Lake Basin. This river is fed by the Merced, Tuolumne, Stanislaus, Mokelumne and Cosumnes rivers. Dams and reservoirs for agricultural irrigation and domestic drinking water suppplies have dramatically reduced the natural flow of the San Joaquin River and its tributaries.
As of 2011, 3.9 million people and more than 100 ethnic groups live in the San Joaquin Valley. According to the California Department of Finance, the population will increase 131 percent by 2050 – the fastest increase in the state. Much of the Valley’s population is clustered in major cities, many dating from the late 1800s when they sprang up during construction of the Central Pacific Railroad. Those communities — Stockton, Modesto, Merced, Fresno and Bakersfield — are part of a string of urbanization along Highway 99, the region’s major intercity corridor. The population here is 5 percent younger than the state average.
The Merced Vernal Pools & Grassland Reserve sits at the edge of urbanization and agricultural fields, about five miles from downtown Merced.
Eastern Merced County includes a remarkably intact section of an alluvial terrace landscape formed along the western base of the Sierra Nevada. At first glance, the region and the site appear to consist of a relatively homogeneous mix of annual grasslands and vernal pools distributed across undulating slopes and occasional low hills. However, on more careful study, one finds this landscape to be quite varied in its soils, geology, and biology. Taken as a whole, this region can provide us with insight into the physical genesis and evolutionary history of a large region of California, including areas well beyond the boundaries of eastern Merced County.
The grasslands of eastern Merced County occur within a region where only about 13 inches of rain falls during the cool part of the year (November through May).
Some of the oldest soils in North America (the China Hat soil formation) are found in the high regions to the northeast.
Proceedings from a 1996 Conference
By Michael G. Barbour
By Carol W. Witham