Low Budget Satanic Cult Horror Movie. Early 70s, Southwestern American Desert Setting.
I saw the first bit on Youtube a few years ago. It was a really low-budget American independent movie probably made between 1970 and 1973. No name actors as far as I recall. It opens with a line of chanting, torch-wielding cultists marching through the desert.
Desert-set Satanic movies it is definitely NOT:
Manos, the Hands of Fate (1966)
Werewolves on Wheels (1971)
The Brotherhood of Satan (1971)
The Devil's Rain (1975)
Race With the Devil (1975)