The pilot stated that he flew for approximately one hour looking for stray cattle on his ranch. He was continuing his search on a mesa ridge when he noticed that the helicopter was losing altitude. The main rotor blades bean impacted 10 to 15 foot high cedars, and the helicopter rolled to the right and impacted the ground. The density altitude was calculated to be approximately 7,938 feet, and the out of ground effect hover capability of the helicopter with these weather conditions was calculated to be 5,200 feet.