Looks like someone invested in Oakland real-estate...
Edit: It ought to be enough with 50-150 km distance to get low land prices around that part of California? Assume a train at 250 km/hour, the commute will be short and there won't be a need for "exotics" (maglev, Musk's tube, etc).
Some will say Acela, but it is only profitable if you ignore capital expenditures.
What if you use the land price increase at the other end of a (quite) fast train to finance building the commute link?