The Vaca Mountains are one of the most prominent landmarks of Solano County, with a steep ridge on the east side that rises abruptly 1,000 feet (305 m) or more above the foothills below.

Because the canyon is difficult to distinguish from most vantage points on the east side, the Vaca and Blue Ridge Mountains present what appears to be a nearly continuous ridge line that defines the west margin of the Sacramento Valley, which is the northern half of the 400 miles (640 km)-long Central Valley of California.

[3][4] The reasonably abundant winter rainfall results in a diverse assemblage of plants, with chaparral stands of chamise (Adenostoma), buckbrush (Ceanothus) and manzanita (Arctostaphylos) on the ridgetops, grasslands with oak trees (Quercus) and poison oak (Toxicodendron) on the slopes, and riparian habitats in canyons with year-round streams.

Bedrock throughout most of the Vaca Mountains are sedimentary rocks of the Great Valley Sequence that are Cretaceous in age (65-145 ma).

These rocks are represented by shale and interbedded sandstone that are thought to have been deposited in a deep-marine setting as submarine fans, sourced by sediment shed during uplift of the ancestral Sierra Nevada.

It is thought to represent remnants from an ancient volcanic eruption on the east side of the Sierra Nevada of an especially fluid flow of lava that spread across a large part of central California.

[1] The Vacas, along with their partners the Pena family, were among the earliest European settlers in the area, being the original holders of the 1843 Rancho Los Putos land grant from Mexico of 44,385 acres (180 km2) that includes most of the southern part of the range.