If you don’t want to take your bike, I would suggest The Path Bike Shop for rentals. They have two locations with the one in Trabucco Canyon closer to trails
https://www.thepathbikeshop.com
If you have time, go introduce yourself on this forum and you will always be able to find someone to ride with and get suggestions.
https://www.imtbtrails.com/forum/
For trails I would suggest Whiting Ranch and the Luge
https://www.mtbproject.com/trail/5066649/whiting-the-luge
or going santiago peak the luge
https://www.mtbproject.com/trail/7045728/whiting-to-santiago-peak-the-luge