Hi Chris
I've not looked for mammals around San Diego but there should be plenty of wildlife in the parks east of the city. I'm not sure what species you're after but Mountain Lion is supposed to be relatively common* in Cuyamaca Rancho State Park along with both California and Merriam's Chipmunk.
Anza-Borrego Desert State Park is good for Desert Bighorn Sheep late morning along with various pocket mice and kangaroo rats.
Just driving around quiet desert roads at night should get you plenty of common stuff (Coyote, Striped Skunks, Raccoons, White-tailed Deer, cottontails, jackrabbits etc), along with some nice reptiles at certain times of the year. Using a spotlight would increase your chances of picking up rarer stuff such as Ringtail, Kit Fox or American Badger, just be careful not to use it in any National Parks or around other traffic, houses etc.
Sorry I can't be more help.
*obviously chances of seeing one still very slim.