Federal investigators are probing whether a helicopter crash that killed four in the Sierra Nevada mountains may have been caused by a lack of markings on a high-voltage power line running across the river canyon.

The crash happened Tuesday afternoon after the Bell 206 helicopter clipped a Southern California Edison transmission line, sparking a blaze that consumed the craft.

Three California Department of Fish and Game scientists and a pilot were killed. The team had been conducting an aerial deer survey.

Federal Aviation Administration guidelines recommend that companies mark and light their power lines according to national standards, so that pilots can spot potential hazards. A SoCal Edison spokesman says that line was not marked.