S. sonomensis is found in three distinct areas in California: the California Coastal Range from Siskiyou to Napa county; from Monterey county to San Diego county; and in the Sierra Nevada foothills.
In California, the species S. sonomensis can be identified in three main regions: the Pacific coastline from north to south, encompassing areas such as the Siskiyou Mountains and Napa County, the Central Coast including Monterey and San Diego counties, and the Sierra Nevada foothills.