On rocky terrain that sees very little traffic, find a flat rock, deposit your feces on it, and toss it off route being conscious of rockfall hazards to others. Dispose of toilet paper as recommended or use natural options. If throwing such a rock seems unsafe, puts feces into a watercourse, or is impossible due to the lack of flat rocks, you have two other options. If a route is not frequently traveled, you can do your duty in a sunny location and smear the feces with a rock, which helps it dry quickly and disintegrate. Alternatively, you can cover the feces completely with a rock or rocks off to the side of the route.
Smears are quick to decompose, but are unsightly and potentially unsanitary.
Hiding the stuff under a rock basically stops breakdown of the bacteria and may also be unsanitary, but will hide mush of the unsightliness from future climbers. Whatever you do, don't leave toilet paper under a rock because it will remain for a long time. On more accessible big walls like those in Yosemite or Zion, it is no longer acceptable to just toss human waste to the base. Instead, place feces in a doubled paper bag and add a bit of kitty litter or lime to reduce odor and absorb moisture. Carry filled paper bags up the wall in a PVC pipe with camps on both ends.