Marie,
Sounds like we have alot in common, as far as this summers trip plan!
Also we visited the Myan ruins in the past and loved them.
My husband and I did several horse back trips , the north rim of the grand canyon-mule trip, it was awesome, Bryce canyon twice on horseback and Zion, all really great day trips.
Just got an add from the Flying Pig adventure co. north of Yellowstone and we are thinking about the Paddle and Saddle trip.
Gwilda