Cathy,

We almost went to SD for a cycling vaca last spring and I still had some sites bookmarked (I had to update a couple of them. Not sure if you mean something like an organized century or regular group rides, but these may give you a place to start:

San Diego Wheelmen -they have weekly rides

San Diego Sierra Club "Bicycle Section"

San Diego Longriders -a century every weekend!

Have a great time. It's really beautiful there! And OF COURSE, good food.