Railway, The Impossible Railroad by Reena Deutsch. This photographic history of the railway from San Diego to Yuma, with stretches in Mexico has plenty of factual data provided to the reader.
The real challenge of the construction was twofold. First, a man big enough to invest 13 million in a venture whose outcome was always in doubt. John Spreckels, who at one time paid ten percent of all taxes in SD County, filled the bill.
Second, the challenge of building a railroad through Carrizo Gorge and up the mountain scarp and down all the way to Dos Cabesas, on the desert floor. The area was isolated, rough and subject to extreme temperature swings. Tunnels were required to keep a low angle for the steam engine powered trains of that era and the rock varied from hard granite to unstable and dangerous. The terrain was subject to flash flooding and earthquakes.
The Goat Canyon trestle was built of wood, because of the temperature swings of 75 degrees during some months of the year. Must read for anyone who aspires to mountain bike or hike down to this monument to man's attempt to engineer a technological solution to withstand the forces of nature.