Sandals are an open type of outdoor footwear, consisting of a sole held to the wearer's foot by straps passing over the instep and, sometimes, around the ankle. While the distinction between sandals and other types of footwear can sometimes be blurry (as in the case of huaraches—the woven leather footwear seen in Mexico—and peep-toe pumps), the common understanding is that a sandal leaves most of the upper part of the foot exposed, particularly the toes. People may choose to wear sandals for several reasons, among them economy (sandals tend to require less material than shoes and are usually easier to construct), comfort in warm weather, and as a fashion choice. Usually, people wear sandals in warmer climates or during warmer parts of the year in order to keep their feet cool and dry. The risk of developing athlete's foot is lower than with enclosed shoes, and the wearing of sandals may be part of the treatment regimen for such an infection. The oldest known sandals (and the oldest known footwear of any type) were discovered in Fort Rock Cave in the U.S. state of Oregon; radiocarbon dating of the sagebrush bark from which they were woven indicates an age of at least 10,000 years.