For tempo work, we used to run on County Road 250, which is the same road used for the Steamworks Half.
If you have a running buddy, park a car at Mile 10, then another at the Missionary Ridge Rd entrance. From the Missionary Ridge rd it's a 3M warm-up to the start line and run to Mile 10. SOLID 10M tempo with mile markers and plenty of shade.
Depending on how early you go, traffic is minimal to nonexistent. LOVED these Tempo's.
Regardless where you get them in, enjoy the hell out of Durango. Love that place.