Tim Fitzharris / Mae Ya Waterfall cascading 260 meters, Doi Inthanon National Park, Thailand

Paul Bertner / River in tropical rainforest at dusk, Tambopata Research Center, Peru

Jeff Foott / Rock formation, Metate Arch, Devil's Garden, Grand Staircase-Escalante National Monument, Utah

Jeff Foott / Round boulders, Theodore Roosevelt National Park, North Dakota

Jeff Foott / Sandstone rock formations, Theodore Roosevelt National Park, North Dakota

Jeff Foott / Sandstone rock formations, Theodore Roosevelt National Park, North Dakota

Jeff Foott / Sandstone rock formations, Theodore Roosevelt National Park, North Dakota

Shane P. White / Opuntia (Opuntia echios) cacti, Santa Cruz Island, Galapagos Islands, Ecuador

Heike Odermatt / River flowing through canyon, Fjadrargljufur Canyon, Iceland

Jeff Foott / Broken Bow Arch, Grand Staircase-Escalante National Monument, Utah

Jeff Foott / Seastack at Harris Beach State Park, Oregon

Jeff Foott / Racetrack Playa with mysterious 'sailing stones', Death Valley National Park, California