The California Rail Pass can be used on any seven days, within a period of 21 continuous days. It doesn't matter what time of day you travel, it will still count as one day of use. Once you've bought your pass, you must use it within one year.
Passengers are not permitted to make more than four one-way journeys within a single route. So for example, if there is no direct route between your start and end station, you can only take four separate trains to make the complete journey.
Reservations must be made by passholders on each train they plan to take; it isn't enough to simply turn up with your rail pass. Hard-copy tickets should be obtain for every route travelled; the pass isn't valid without an accompanying ticket. Tickets can't be bought onboard, so make sure you buy them in advance.
The California Rail Pass entitles passengers to regular seated travel. You can upgrade to Business Class or Sleeping Accommodation for an additional fee (payable at time of ticket reservation).
Refunds for rail passes will only be issued if the pass hasn't been used, and the pass as well as any tickets are returned to Amtrak. If you've pre-booked sleeping accommodation, you may be charged if you cancel within seven days of your scheduled journey.
Unfortunately, rail passes cannot be used in conjunction with special offers (unless it says so in the offer conditions).