Data collected and processed by U.S. Geological Survey, in cooperation with the U.S. Army Corp of Engineers, Southwestern Division, Little Rock District. Data were collected by R.J. Huizinga, B.C. Rivers, D.V. Grant, D.J. Fazio, E.M. Lindroth, A.L. Walsh, K.M. Hubbs, A.R. Whaling, S.C. Bradford, K.R. Cothren, S.L. Hunter, M.L. Phillips, K.A. Smith, and Z.S. Bordovsky. Preliminary data processing was done by B.C. Rivers, A.R. Whaling, and K.A. Smith, and final processing and compilation was done by B.C. Rivers, R.J. Huizinga and J.M Richards.