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SALINAS VALLEY WATERSHED
The Salinas Valley lies within the southern Coast Ranges between the San Joaquin Valley and the Pacific Ocean. The Salinas River and its tributaries, which make up the Watershed, drain the valley. It extends approximately 150 miles from the headwaters to the mouth of the river at Monterey Bay. The total drainage area of the basin is about 5,000 square miles.
The major land uses in the Salinas Valley are agriculture, rangeland, forest, and urban development. In general, forest lands are on steep slopes, rangelands are in rolling to steep hills, and agricultural and urban development are in areas where slopes are gentle, especially near the Salinas River and its tributaries. Agriculture is the primary water use in the basin and is most intensive near the coast between the city of Salinas and Monterey Bay, where land is devoted primarily to vegetable production. Less land is under cultivation south of King City, where the major crops are grain and wine grapes. Most of the water used in the basin is ground water withdrawn near where it is used. No water is imported, and all recharge originates as precipitation in the drainage basin.
The Salinas Valley lies almost entirely in a northwest-trending structural trough filled principally by unconsolidated continental deposits. The valley is bounded by the San Andreas Fault on the northeast and by a series of aligned and interconnected faults on the southwest. The mountains that bound the valley were formed by uplift and deformation caused by crustal shortening and are underlain by consolidated marine sediments, intrusive igneous rocks, and metamorphic rocks.
The Salinas drainage basin is bounded on the south by the La Panza Range, on the southwest by the Santa Lucia Range, and on the northwest by the Sierra de Salinas; the 200-mile- long Diablo Range and the shorter Gabilan Range bound the basin on the northeast. The mountains that form the northeastern, northwestern, and southwestern margins of the basin slope steeply and are dissected by streams that have carved steep canyons into the valley walls. The southeastern margin is characterized by gently rolling hills and broad valleys.
The Salinas Valley is about 30 miles wide in the south, about 20 miles wide in the middle of the valley, and about 10 miles wide in the flat lowland areas north of Greenfield. The valley floor has an altitude of about 1,200 feet at Santa Margarita in the south and about 400 feet at San Ardo, and is near sea level at the shoreline of Monterey Bay. Stream gradients are relatively steep in the southern headwater region, and the valley floor is deeply dissected by the streams. As the valley becomes less steep from near San Ardo to Monterey Bay, stream gradients lessen also, and the tributary drainage area becomes smaller.
Climate in the valley is Mediterranean and is moderated by the Pacific Ocean; summers are mild and winters are cool. Precipitation is almost entirely rain, which falls mostly in late autumn, winter, and early spring. Little rain falls from May through October; 87 percent of the yearly total falls from November through April. Average annual rainfall ranges from about 12 to 40 inches within the basin and depends mainly upon altitude. Rainfall on the valley floor ranges from about 12 inches near the center of the valley to about 16 inches near the base of the surrounding mountains.
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