You would be amazed what the maps tell:
- The 1910 and 1920 maps show only rail lines; the 1949 map shows roads and rail.
- The earlier maps show how many tracks are on each route; the 1949 map only shows the routes.
- The 1949 map shows which rail lines are transit routes and which are used only for freight. If I read the legend right, the area served by the trollies had retreated back to its 1910 range, only without the density.
- The 1949 map shows what many people viewed a the benefits of busses over trollies. Where one line did all the business between Covina and San Bernadino in 1920, you had three bus lines covering the whole of the corridor in 1949 with convenience added in the mix. Busses also gave a direct transit connection between San Bernadino and Orange
County --a routing which would have been costly and bled red ink as a trolly line. Also note the area to the east of the Watts/Compton/Dominguez mainline
- As interesting as the expansion of service via busses is, it's also interesting to see where the service was cut back. Redlands was now only an end stop (instead of a local transfer point), everything south of Inglewood had been abandoned (no buses, even) and Pasadina had become merely part of a loop (instead of a center of its own area and gateway to Mount Lowe and a view of the basin).
The automobile would cause greater changes from here, however. The expansion of the Suburbs into and beyond the settled areas served by the rails and busses would cause traffic jams, and the busses would be subjected to traffic jams that even the trams wouldn't suffer from. Further, a grid of Expressways would develop, obviating the futility of bus usage for all but the poor and stubborn.
Eventually the need for a rail option on its own right-of-way would become known, and (only in America) would the idea of "the cheaper it is, the better quality it is" would lead to corners cut on the light-rail.
Still, it's interesting to see what had happened, on what was one of the best urban rail transit systems in the nation (in a place one would hardly believe it could have existed, in addition).