With a wood fired boiler you could make power with without petroleum. Have to manage that pressure vessel pretty carefully though...
Steam generation and regulation is almost a lost art for the single person, and a PTO generator needs 540RPM of upwards of 10hp. Would almost be better to have an old tractor engine converted to run on natural gas or ethanol.
Depends on what is a natural resource, myself if I were to build a totally steam powered engine it would be fueld by pellets, pellets can be fed by an auger tube as per demand, pellets can be made from an extruded cellulose mixture of ground up garbage that has been sorted so its all materials that can be shredded, mixed into a slurry in a portable concrete mixer, fed through a large grinder identical to a meat grinder and the pellets looking like rabbit feed are then dried and used as fuel. Or to be used in a still for ethanol, or both.
That is just off the top of my head.