Some very helpful information, thank you! Based on what's been said it sounds as though I'd ride West to East, either leaving my auto at the parking garage near the Amtrak station in Pittsburg or parking at Great Falls Tavern Visitors Center (after verification). The latter might be a better option (like mbusky) if I need to make a reservation for the bike, as I'd have more control of the first day as opposed to making sure I stayed on schedule and caught the train coming back.

Edit - the Great Falls Visitor Center is closed, so....other options like parking in downtown Pittsburg.