The western terminal of the Pony Express is in Sacramento, as is the end of the Pony Express Bikepacking Route. Even so, the first eastbound XP rider left from San Francisco, the celebration for the first arrival of the westbound mail was held there, and a lot of the westbound mail was delivered the The City (as it was and to some still is known).
For the most part, Pony Express mail between San Francisco and Sacramento went by steamboat. Occasionally, however, the westbound rider arrived too late to make the once-a-day steamboat connection. So on twenty occasions, westbound riders crossed the Sacramento River and rode on toward San Francisco.
There are numerous monuments marking the stops west of Sacramento, none of which XP Bikepacking Route riders will see unless they make a special trip. The first one, Solano House, is on the campus of the University of California, Davis, just a few miles from where I live. I rode out there today (November 27, 2020) to get a picture. It is located here.
I know of at least two others relatively close, one near Dixon, the other in Vacaville. As I rode out to the Solano House marker, I thought I might make a project out of visiting all of the monuments west of Sacramento. When I returned home, however, I found this page, which lists 79 XP monuments in California. Of these, 22 lie west of Sacramento. So I may not hit all of them. But I will post what I do get pictures of on this blog.