Have you ever looked at a rail map?

California and Indiana both had a population of about 2.7 million in 1916. Indiana had a dense rail network and California didn't. Indiana is only ~5x smaller than California.

This is what the rail network looked like in 1916:

https://etc.usf.edu/maps/pages/4400/4401/4401.htm

The less dense areas are impassable mountains or inhospitable desert