i don't fish cachuma, but i use mini jigs at chabot and how you find the depth their at is i simply drop my jig to the bottom, jig for a while if there are no bites you reel up a little and keep jiggin' till you get a bite then you now the depth they're at.
Cachuma is seriously depleted of crappie. It's worth the time to go to Lopez as they are wide open on Chartruse 1 inch curley tail grabs or anything in that color right now. Cachuma hasn't been worth spit for crappie in years...My .02 KelDawg