Western States National Historic Trail Study Act of 2013 - Amends the National Trails System Act to require the Western States Trail, a trail of approximately 100 miles from Squaw Valley to Auburn, California, along which are conducted the Western States Trail Ride and the Western States Endurance Run, to be studied for designation as a national scenic trail. Requires such study to include a determination as to whether the Trail is appropriate for designation as a national historic trail.