Provenance Sources: Top left: Antelope Canyon, Arizona. Source: Photo by <a href="http://ingomeckmann.com">Ingo Meckmann</a>. Used with permission. All rights reserved. Bottom left: Braided drainage near confluence of the Yukon and Koyukuk rivers. Source: Figure 35, U.S. Geological Survey Professional Paper 835.ID. Pewe, T.L. 849, Digital File:ptl00849. Bottom right: Sand ripples at Llanddwyn. Source: photo by RICHARD OUTRAM from Wales (Llanddwyn, Uploaded by PDTillman) [<a href="http://creativecommons.org/licenses/by/2.0">CC BY 2.0</a>], via Wikimedia Commons
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