Park officials say another visitor reported seeing the 32-year-old soldier, who was not named, fall from a 300-foot (91-meter) cliff on Wednesday evening.
Officials say he had climbed over a metal railing at Steaming Bluff overlook to get a better view and the ground beneath him gave way.
He was found more than two hours later seriously injured on a narrow ledge about 70 feet (21 meters) from the edge and flown by helicopter to a hospital.
Hawaii News Now reported Thursday that Army officials say the soldier was stationed at Oahu's Schofield Barracks and training on the Big Island.
Information from: KGMB-TV, http://www.hawaiinewsnow.com/