Santa Clara Valley

Geology & Topography

Santa Clara Valley was formed in the Cenozoic Era, when the earth’s tectonic plates moved into the positions in which we find them today. Movement of the Pacific Plate against, and under, the North American plate pushed up mountains, including the Santa Cruz Mountains on the west of Santa Clara Valley, and the Diablo Range on its east. Geologically, those ranges are sedimentary, consisting of ancient sea floor.

The benches, and parts of the valley floor, very close to the hills,  consist of alluvial deposits left by water streaming down the hills. Low-altitude areas, especially those closest to the bay, feature deep, fine soils formed of sediment from times when the bay covered much more land. The last of these times was only several thousand years ago.

Climate

The entire AVA has a warm-summer Mediterranean climate. Mesoclimate differences are based on three primary factors: altitude, distance from the ocean and bay, plus the ease with which breezes from those bodies can reach the area in question. In general, the further south or east the area, the warmer it is, due to distance from the water.

High-altitude areas will be a little cooler for most of the day, but warmer than the valley floor at night and in the early morning. Frost can be a risk during spring in the lowlands. Fog is not a factor.

Two notable mesoclimates are the San Ysidro District AVA and the Hecker Pass area. San Ysidro district is east of Gilroy. The Hecker Pass is just north of Gilroy, on Highway 152. In both cases, there are avenues for cooling breezes from Monterey Bay, which moderate their temperatures much more than in surrounding areas.