Orthotrichum (Orthotrichaceae) is a species-rich genus of mosses in California. The last key to Californian Orthotrichaceae was produced in 2004 and included 35 species. Since that time, new discoveries have been made, and new identification tools are being posted on the site called the California Moss eFlora. As a model for the eFlora, I created an updated key to Orthotrichaceae in California with photographs at each couplet. I included 47 species known from California and adjacent states. My key will be useful in verifying the thousands of Orthotrichum specimens currently housed in herbaria. Species distribution maps produced after verification of those specimens could allow for tests of hypotheses regarding the biogeography of Orthotrichum in California.