The western and southern slopes, on the other hand, are drier and warmer, leading to fewer dense woodlands and more chaparral, grassland and oak savannah.

In the Miocene era, precipitated by the combination of tectonic movement due to the seismically active environment and the presence of magma not far below the Earth's surface, a massive period of uplift ensued.

[3] These are generally areas of 15 to 30 percent slopes that support dense mixed oak woodland, with large percentages of California laurel and bigleaf maple.

The upper western reaches of Sonoma Mountain have some amounts of the Raynor clay association, which group typically has a depth to bedrock of about four to five feet.

Lower on the western exposures, along the Lichau Creek immediate drainage area, there is a broad occurrence of Goulding clay loam on slopes of about 15 to 25 percent.

In these oak woodlands, the dominant understory plants are toyon, blackberry, western poison-oak and in occasional drier patches some coyote brush.

The land was purchased for public use between 2003 and 2015 by the Sonoma County Agricultural Preservation and Open Space District in cooperation with the Coastal Conservancy and Bay Area Ridge Trail Council.

A diverse fauna inhabits this area including black-tailed deer, coyote, bobcat and mountain lion; moreover, there are abundant avifauna, amphibians, reptiles and insects.

Copeland Creek and its tributaries drain the preserve as they wend their way down steep ravines toward eventual discharge to the Laguna de Santa Rosa.

The property was originally a Spanish Land Grant holding and is now owned and managed by Sonoma State University, who uses it as a research base and as an educational tool for the general public.

The preserve is situated at elevations between 1,600 and 1,900 feet (490 and 580 m) above sea level and features a landscape riddled with basalt exposures that betray the volcanic prehistory of Sonoma Mountain.

[10] The TV broadcast antenna for KRCB was located on Sonoma Mountain from the station's start-up in 1984 until it moved to Sutro Tower in San Francisco in 2019.