On July 26, 2004, about 1421 Pacific daylight time, a Bell 206B, N549W, collided with trees and terrain while maneuvering about 4.9 nautical miles southeast of Little Valley, California. The helicopter was operated by Aris Helicopter, Ltd., Moffett Field, California. Visual meteorological conditions prevailed during the aerial survey flight for the California Department of Forestry (CDF), and a company flight plan was filed. The helicopter was substantially damaged during the impact sequence and was subsequently destroyed in the post impact forest fire. The commercial pilot and one passenger were seriously injured; the second passenger sustained minor injuries. The flight was performed under the provisions of 14 CFR Part 91, and it originated from Fall River Mills, California, about 1402. According to the CDF Aviation Safety Officer who responded to the accident site, the purpose of the flight was to provide the two CDF passengers with an aerial mapping opportunity around active fire areas in the Lassen National Park. Ground-based witnesses observed the helicopter flying between 50 and 75 feet above ground level, in a downwind direction, over the 5,100-foot mean sea level (msl) upsloping terrain. The surface wind was from the north-northeast, about 10 knots. The helicopter was flying on a southwesterly course, toward the crest of a mountain. The temperature was almost 90 degrees Fahrenheit. The witnesses further reported that the helicopter's engine was operating until it impacted trees, about 20 feet beneath the mountain crest. The pilot indicated that his specific mission on the accident flight was to maneuver the helicopter over a route that would provide the front seat passenger the opportunity to accurately mark global positioning satellite (GPS) waypoints around the perimeter of the fire area. Initially, the pilot flew at 6,500 feet msl, but when the passenger started marking waypoints, the pilot descended to 5,500 feet msl. The pilot further indicated that during the flight he made several turns. Just prior to the crash, he flew in a southerly and then a northerly direction. The pilot reported that when he turned to an east-southeasterly direction, he "pulled in as much collective as [he] could...," and he observed his proximity to the fire line. Thereafter, he directed his attention to a hill that he was approaching. The pilot indicated that he had expected to be higher than the top of the hill, but he was lower. At this time, despite his efforts to increase altitude, the helicopter impacted trees and terrain.