Sundays are seasonal and only open from October through May.Fun with the Family Tri-A-Bike is the oldest bike rental company west of the Mississippi. You’ll find mountain and road experts here able to answer your questions about exploring the desert terrain. Tri-A-Bike rents assorted bikes (including mountain, road, tandem, and kids’). Kids too young to ride? Tri-A-Bike has a trailer to pull the little ones.