P.G Schruben

• Geology and resource assessment of Costa Rica at 1:500 000 scale : a digital representation of maps of the U.S. Geological Survey's 1987 folio I - 1865 / by Paul G. Schruben
• Geology of the conterminous United States at 1:2 500 000 scale : a digital representation of the 1974 P.B. King and H.M. Beikman map / by Paul G. Schruben [and others]