Jon E. Spencer, Karen J. Wenrich and Trevor Cole report that a breccia pipe is a vertical, pipe-like mass of broken rock (breccia), typically a few tens of meters across and hundreds of meters in vertical extent. Breccia pipes formed within Paleozoic and Triassic strata over a broad area around the Grand Canyon, and later some contain high-grade uranium ore was introduced by groundwater (Wenrich and Titley, 2008). They were created when groundwater (possibly basin brines), flowing through Redwall Limestone dissolution breccias and along fracture zones, dissolved more limestone, causing collapse of overlying rocks and possibly creating sink holes.
Some pipes extend many hundreds of meters upward into the Chinle Group (formerly Chinle Formation; Heckert and Lucas, 2003), indicating that some pipes are at least as young as this Upper Triassic rock unit (Brown and Billingsley, 2010). Some pipes are blind and never broke through to the surface. Breccia pipes are abundant in the Grand Canyon region, with at least 1300 pipes or suspected pipes identified (Sutphin and Wenrich, 1989; Brown and Billingsley, 2010). These breccia pipes have been of interest both for their economic value and because they are adjacent to Grand Canyon National Park and the Colorado River (Spencer and Wenrich, 2013).
Three datasets are included as shapefiles in this publication, as well as an Excel Workbook containing the three datasets and a pdf file of a geologic map of northwestern Arizona showing the locations of breccia pipes, collapse structures that might be breccia pipes, and circular features that might be collapse features or breccia pipes (all of which are known or possible breccia pipes). Each dataset is a set of points representing breccia pipes or possible breccia pipes identified on the Colorado Plateau.
Some circular features are identified by more than one map, so the total number of identified features in all three datasets is less than the sum of the features listed in the databases (3286). In many cases it is not known if the features are in fact breccia pipes or are younger and shallower features such as sinkholes. Because of this uncertainty, many such features are labeled “collapse structures” on geologic maps, which is not specific about the depth or age of the feature. In addition, most breccia pipes have not been drilled and it is unknown if they are mineralized at depth.
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