What are the projection, horizontal and vertical datum, format, and distributed tile extent of contours?

Contours are not projected, but are provided in geographic coordinates (latitude and longitude) in units of decimal degrees, and horizontally referenced to the North American Datum of 1983. Contour elevation values are vertically referenced to the North American Vertical Datum of 1988. Contours are staged in either Esri File Geodatabase 9.3.1 or 10.1 format, or as a Shapefile, and are distributed in 1x1 degree tiles for the conterminous United States.