Willetts and Sespe... Los Padres, southern region. Maybe further than you want to go. There are also hot springs to hike to around Santa Barbara but Willets and Sespe are more remote.
There are some very helpful books about hot springs, one devoted entirely to the west (California/Nevada/Arizona/NM).
I'm going to Mono Hot Springs in a couple weeks... it's in the Sierras near Huntington Lake.
And then there is www.soak.net....