The contours were drawn with information on elevation, geologic outcrops and wells drilled as of 1998. This is a Vector data set. The horizontal datum used is North American Datum of 1927. The ellipsoid used is Clarke 1866. The semi-major axis of the ellipsoid used is 6378206.4.
Negative values indicate below sea level.
A value of 9999 indicates that the contour is not a multiple of 500. A value of 'Y' indicates that some interpretation was involved in drawing the contour line. Compilation of this data set and the associated metadata was funded in cooperation with the South Dakota Department of Environment and Natural Resources and the West Dakota Water Development District. Janet Carter U.S. Geological Survey Hydrologist 1608 Mt. View Rd. West Dakota represents various local and county cooperators.