Race With The Devil
1975

Roger Marsh and Frank Stewart, and their wives Kelly and Alice, camp their RV in a desolate part of Texas en route for a vacation in Colorado. While there, they witness a satanic ritual where a woman becomes a human sacrifice. They are spotted and barely manage to escape with their lives.

They report the incident to the local sheriff who seemingly investigates but tries to suggest that what they probably saw were some hippies killing an animal. It beomes clear that the sheriff is part of the satanic cult.

Before they leave, Roger steals a sample of the murder victim's blood with the goal of delivering it to the authorities in Amarillo. As they journey towards Amarillo they find themselves pursued by a growing number of satanists networked throughout Texas.