Answer:
Before the gold rush, the west was wild, and there were fewer individuals around. The large urban communities in California were shires with a couple of hundred natives. While the large harbors got perhaps 2 - 3 ships, every week before the surge, there were dozens of boats a day once gold was found.
The railways would turn into the best drivers of westbound development since they brought individuals west and permitted the things they created to be sent east.