Here’s something I had been waiting for a chance to quantify. Dian Schaffhauser writes:

Type “sonoma” and “mission” into books.google.com and choose “Full view” to eliminate those books that haven’t granted permission to be fully displayed or that are still in copyright because they were published post-1923. About 550 titles show up…

Or try it from the frozen wastes north of the 49th parallel, and 166 titles show up. Google is so careful about copyright, it hurts.