Leg press, deadlifts, RDLs, lunges, leg extensions, leg curls, hack squats, split squats. All those will hit your legs, plus there variations. Do some sprints, run hills, stairs, those will hit your legs. Im sure there are more lifts I can't think of this second as well.
While natural gas occurs in nature as a mixture of methane and other gases, propane is actually a byproduct of both petroleum refining and natural gas processing.
Propane is a cleaner burning fuel emitting fewer greenhouse gasses. Propane is not a greenhouse gas in its natural state. Propane has higher octane rating reducing the tendency of knocking, evident in some petroleum/diesel engines. Propane is much cheaper to purchase than gasoline or diesel. Propane is nontoxic and not detrimental to soil or water if accidentally spilled.