The flight instructor reported that, after conducting flight maneuvers during an instructional flight, he and the pilot receiving instruction proceeded to sightsee around mountainous terrain at 800 to 1,000 ft above ground level. He added that, after the pilot receiving instruction maneuvered around rising terrain, the airplane was moving toward "fairly significant" terrain. The flight instructor reported that "it was assumed" that the airplane had the necessary performance to climb over the rising terrain ahead, but he soon realized that the airplane was in a "box canyon" and would not be able to climb above the rising terrain. The flight instructor took the flight controls, "pitched the aircraft up to stall speed," and the airplane impacted trees. The airplane sustained substantial damage to the right wing. The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.