Out in the desert, off the 8 east, just past Jacumba but not quite to Ocotillo, there is/was a place up in the hills called Shell Canyon. I was just a little kid then, but I found a perfectly formed fossilized double clam shell there. Didn't know there were other places -- whereabouts in San Diego?
If you’re familiar with San Diego, it’s where Home Avenue runs from the freeway to the turnoff to Fairmont. Home Avenue runs down the middle of a canyon and it was on one of the elevations overlooking the canyon above where a Goodwill store is (or used to be— it’s been a while since I’ve been there).