Hikers walking through cactus trail, Volcan Santa Ana, 2365m, Parque Nacional Los Volcanoes, El Salvador, Central America

Close up of Engelmann's prickly-pear (Opuntia engelmannii) cactus in bloom, Watchman trail, Zion National Park, Utah, United States of America, North America

A sign along the Bright Angel Trail in Grand Canyon warning that the plants in this area are very fragile, Grand Canyon National Park, UNESCO World Heritage Site, Arizona, United States of America, North America

Woman nordic walking, Apache Trail, Arizona, USA

Cactus plant growing beside an outhouse, San Diego, California, USA

Panoramic view of an array of cactus plants, San Diego, California, USA

Panoramic view of an array of cactus plants, San Diego, California, USA

Cactus plant growing beside an outhouse, USA

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Man and woman backpackers hike on the popular Peralta Trail in the Superstition Wilderness Area, Tonto National Forest near Phoenix, Arizona November 2011. The trail offers spectacular views of Weavers Needle and the rugged Sonoran desert.

Bonni Casteel carries her bike over an un-rideable part of a singletrack trail in El Potrero Chico Park in Mexico. El Potrero Chico means "The Little Corral". It is part of the Sierra Madre occidental and used to be under the sea. It is a unique geologic limestone formation with cliffs up to 2000 ft. high.

Woman rides the Submarine Rock Loop in South Sedona, Arizona. The trail has everything from slickrock to single track to stairs that lead to Submarine Rock.

Woman runs the Cathedral Rock Trail in Sedona, Arizona May 2011.

Woman trail running in Usery Mountain Park, Phoenix, Arizona November 2011.