Looks like C.oreganus abyssus but could be concolor. Was it east or west of Lake Powell? West of lake powell snakes are C.o.abyssus. They go north into Utah to the vicinity of Escalante and the Kaiparowitz Plateau. East side are C.o.concolor. C. viridis is sympatric with concolor on the east side but that snake id definitely not viridis.

Also, FYI, nuntius (Hopi's) have been sunk, there is indeed a separate nuntius clade but it does not differ enough from nominate viridis to qualify as a subspecies. The nuntius clade is endemic to Az. Utah snakes are all of the nominate C.viridis viridis. Size and color are habitat related and have nothing to do with "nuntius" or "viridis" clades. Here in Az. one can find a small 24 inch "nuntius" in one habitat and just few miles away in a different habitat find a 4 ft. green "nuntius". Likewise there are stunted 2 ft. reddish viridis in west Texas.

Rich