I stopped at a Pemex to buy some tacos and tried to pay with some 10 peso bills that were given to me by a friend that was in Mexico about 20 years ago. It turns out that the bills are no longer valid. The manager of the Pemex began apologizing and I could not figure out why. The it occurred to me that he thought I had received the bills from a Mexican who was trying to pass them to me as change. I told him this was not the case, that a friend had given them to me. A collector of old bills overheard our conversation and bought the bills from me at face value!
I was planning on staying at Monclava but I forgot that Mexico does not do the whole daylight savings time thing and I had another hour to go. So I rode to Saltillo. The ride on 57 is fairly boring and this was really the only scenery on that stretch of road.
My Spanish class has paid off already. I went out to eat this evening and locked my key in my room. I was able to explain this to the receptionist, in Spanish, and get my room opened.
I don't know how far I will get tomorrow, but stay posted.