Used to mark the trails of most reservations and state parks, trail blazes are the spray painted savior of the lost hiker. Most parks have multiple trails throughout their stretches, and will designate to each of them a color (blue, red, yellow, white, and orange are the most common). More extensive parks may have multiple trails of the same color, i.e. a blue trail at the northern and southern sections of the park. As of late, a trend has been growing to blaze different trails with different shapes (rectangles, triangles, squares, and diamonds) instead of the sometimes confusing color blazing. The following is a complete list of the trail blazes one may come across and their meaning.
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Start of Trail
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Straight Ahead
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Left Turn
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Right Turn
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End of Trail
With careful noting and following of all trail blazes within a national/state park you can be ensured of reaching any scenic destinations, not getting lost, and returning home safely. Blazes will often be found on trees roughly at eye level or on large barren rocks. Trail blazing began by early travelers stripping small squares of bark off of trees, and evolved to hikers painting the symbols when they realized the stripping killed the trees in a short period of time. Today trail blazes ensure a satisfying experience on all of your hiking adventures.
Sources
http://www.bikeguy.net/akeyto.htm
http://members.aol.com/Time2Hike/blazes.html
Pyramid Mountain Natural Historical Area hand guide
My own hiking experiences