In consequence of the uplift the third major event, the present cycle of erosion, was initiated. The streams became strong and swift and so were able to cut deeply into the underlying rock and carry away the land waste. In this process the streams have removed many cubic miles of rocks, which, if replaced, would fill the present canyons and build up their bordering land to the level of the lofty Markagunt and Paunsaugunt Plateaus. The gigantic features of Zion and Bryce Canyon National Parks mark a stage in the process of erosion that began long ago and which, if continued without interruption, will convert the present rugged landscape into plains near sea level. _Distinctive Features of Bryce Canyon._—In its regional setting Bryce Canyon National Park is the southeastern border of the extensive Paunsaugunt Plateau. It comprises two areas of strongly contrasted topography that meet in a line that marks the rim of the plateau and the top of its bordering cliffs. Back from the rim the plateau surface on which the park buildings and the automobile roads have been constructed is generally flat land traversed by broad, shallow valleys in which erosion is inconspicuous. Below the rim erosion has produced a region of remarkable ruggedness. It might naturally be supposed that the beautiful amphitheater at the head of Bryce Canyon had been carved by waters pouring down from the plateau above. But the plateau streams contribute nothing; they flow away from the rim. The chief sculpturing agents are the rain and snow that fall directly into the canyon. In producing the amazing variety of erosion features the streams have been aided by frost that pries fragments from the cliffs and by chemical agencies that decompose the rock and supply its vivid color. The development of the park landscape was made possible by movements within the earth’s crust which brought originally low-lying strata to an altitude exceeding 8,000 feet. Streamways on the flat top of this uplifted block were little affected, but with greatly steepened gradients the streams around the borders of the newly made plateau became powerful. The Paria and its swiftly flowing tributaries have cut deeply into the face of the Paunsaugunt and carried billions of tons of ground-up rock to the Colorado. At the present time erosion by Bryce Creek, Yellow Creek, Willis Creek, Podunk Creek, and many smaller streams, is causing the plateau face to retreat northwestward, and these streams are taking into their drainage areas channels that formerly carried waters northward to Sevier River.