On Sunday, June 23, 2013, two friends, ages 40 and 38, set off an overnight backpacking trip at the Ten Lakes trailhead. Their destination for the night was one of the Ten Lakes, a six-mile hike. Of the pair, one lives in the Yosemite area and has some limited backpacking experience in the park, while the other had never before been on an overnight backpacking trip. Neither hiker had ever been on the Ten Lakes Trail. The local backpacker brought along a full-park topographic map (scale 1:80,000) that, though it included the area they would be hiking in, was not detailed enough for finding their way if they were to lose the trail. The local backpacker also was relying on his cell phone’s compass for any navigation the pair might need to do.
http://www.nps.gov/yose/blogs/Backpackers-Get-Lost-Near-Ten-Lakes.htm