The Peace Killers(1971)

Overview:

Siblings Kristy and Jeffrey are buying supplies at a remote desert gas station when some members of a biker gang come cruising in. The bikers recognize Kristy, who used to be the main squeeze of the gang's leader before she ran away. The pair get away, but the bikers find out that they're living in a nearby commune, and start making their battle plans to bring Kristy back.