From the back of the 128-page sourcebook:
"California was making it through the Reckoning about as well as anywhere in the Weird West, right up until the Great Quake of 1868, which tossed most of the state into the sea, forming the now-legendary Great Maze. The ghost rock in the Maze's channels brought settlers by the thousands to the mysterious center of trade in the Maze: the City of Lost Angels.
Recently, city founder Reverend Grimme and his Church of Lost Angels kicked the unfaithful out of the city and started on a grim crusade to convert the rest of the Weird West over to their way of thinking - or else!
Lost Angels is packed with details on the surface and secrets of Grimme's celestial city. It's also got new rules for mestizo Anahuac priests, plus some Marshal's guidelines for a macabre new branch of scientific weirdness known as patchwork science, and it's capped off by a wild adventure that ties it all together.
It's the heroes' paradise - to lose!"