I saw this from the air while flying out of Sacramento this morning. It's clearly an abandoned dirt track, there are some paved roads and evidence of buildings and parking that are no longer there. I could find nothing "on-line" about it, though.
I don't think it's in use anymore, when I saw it from the air, it was much more "worse for wear" than even in these two pictures. Thanks for tracking that down!
Abandoned, Sports - Misc 
It is (was?) an equestrian park. Two Jakes Park equestrian facility.
- Jake