If you do have another hour or so you can book a tour up to the top of the mesa to a pueblo which has been inhabited from around 1100 AD and was a thriving city when Coronado came through in the 17th century. The Mission Church of San Esteban del Rey, completed in 1640, still dominates the plateau.
Your conducted tour takes you through the streets of the village and allows time to view and purchase the lovely and quite reasonably priced thin wall pottery.
There are over 300 adobe houses on the mesa top and they are owned by Acoma females, who pass them on to their youngest daughters.
but those looking toward the massive Mount Taylor volcanic cone are particularly fine.
If you want to have time for the tour, a snack, and a chance to view the museum allow yourself at least three hours at the pueblo. For lots more pictures of our Arizona trip go to http://www.flickr.com/photos/83918664@N00/