The pilot reported that during an "introductory flight" for two passengers, he departed the airport and flew into a canyon where the airplane encountered an "unforeseen immense downdraft". He further reported that he immediately initiated a right turn to exit the canyon but it became clear that a turn was not possible due to the mountainous terrain. Subsequently, the pilot decided to make an emergency landing on a mountain road. After touchdown the airplane skidded off the dirt road and down an embankment. A post-crash fire resulted in substantial damage to the fuselage and both wings. The pilot reported that there were no pre impact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. As a safety recommendation the pilot reported that he should have given himself more altitude before entering the canyon.