Source Report: http://repository.azgs.az.gov/sites/default/files/dlio/files/2010/u15/DGM-52DepthToBedrock_Report.pdf

The line feature represents estimated depth to bedrock contours for the state of Arizona. Except for depths based on bedrock penetrations reported in bore holes, determination of depth to bedrock is based on interpretation of geophysical data, and solutions for bedrock depth are in general poorly constrained. As discussed above (in the report) the definition of 'bedrock' is subject to interpretation. These contours should be considered qualitative. Horizontal accuracy of depth to bedrock contours cannot be rigorously quantified, but is estimated to be in the range of +/- 1-3 km. Depth estimates are poorly constrained and should be considered highly uncertain, in the range of +/- 20-30 percent, except in the vicinity of wells penetrating bedrock. Depths are reported and contoured in feet, following common practice in virtually all of the available source data.