Elevation data from USGS GTOPO30 Digital Dataset.
GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometre). GTOPO30 was derived from several raster and vector sources of topographic information. Detailed information on the characteristics of GTOPO30 including the data distribution format, the data sources, production methods, accuracy, and hints for users, is found at the GTOPO30 Readme File http://edcdaac.usgs.gov/gtopo30/README.html
GTOPO30, completed in late 1996, was developed over a three year period through a collaborative effort led by staff at the U.S. Geological Survey's EROS Data Centre (EDC).
http://edcdaac.usgs.gov/gtopo30/gtopo30.html