California chiles are dried Anaheim chiles and closely akin to the New Mexico chile which is also a dried form of the fresh Anaheim chile. These chiles are quite mild, about 500 on the Scoville heat scale as opposed to the New Mexico red chile which is closer to about 2500.
California chiles are typically used in mild sauces or additions to soups or stews. They make a nice mild enchilada sauce or you can combine them with other chiles for a more complex sauce.
Look for these chiles in a Mexican market or even in some large stores with diverse foods such as Walmart. You can also buy California Chiles online, here at Gourmetsleuth.com. We sell them in 8oz bags, freshly hand packed.