I selected San Mateo County for this search to demonstrate the return because I am familiar with the area, and because your riding discipline may be a fit for Woodside, Portola Valley, and thereabouts.
The Coastside and East Bay may also be locations to pursue.
I am undisciplined and unqualified to direct you to specific boarding locations.
Horse facilities in the Bay Area are tucked in nooks and crannies.
A short distance as the crow flies or as appears smooth on a map can be a long and knarly drive.