I never did get down to Stockton for the expanded shale. I've read enough reviews that I'm sure it's a wonderful media, but I have been using pumice for several weeks now and it is great. I was able to find it just north of Chico at Kinney's Nursery. It's used to lighten and hold hydration in soil. Here's a link to my review of pumice on my blog. California is a major producer of pumice so it should not be too hard to find.