A ﬂatiron is a tilted, triangular rock outcropping, usually on the ﬂank of a mountain, a type of hogback ridge composed of coarse sandstone and conglomerate. Flat-lying sedimentary rock is pushed upward by geological uplift, creating a core area edged with steeply uplifted sedimentary rocks. Water erosion cuts through the uptilted edge, forming a series of V-shaped valleys with triangular rock masses in between, resembling a smooth row of sharklike teeth. The name comes from the fact that the triangular slabs resemble the irons used to press clothes. Some of the best-known ﬂatirons are found near Boulder, Colorado, where they tower above the town on the east-facing ﬂank of the Front Range. Others are found in the Garden of the Gods in Colorado Springs, Colorado. Flatiron has an architectural application, as well, as in the Flatiron Building in New York.