drawing in the National Gallery of Art (NGA 15118)

drawing in the National Gallery of Art (NGA 14797)

drawing in the National Gallery of Art (NGA 13510)

drawing in the National Gallery of Art (NGA 13368)

drawing in the National Gallery of Art (NGA 14031)

drawing in the National Gallery of Art (NGA 14033)

drawing in the National Gallery of Art (NGA 14043)

drawing in the National Gallery of Art (NGA 15187)

drawing in the National Gallery of Art (NGA 13123)

drawing in the National Gallery of Art (NGA 13395)

drawing in the National Gallery of Art (NGA 13396)

drawing in the National Gallery of Art (NGA 13703)

drawing in the National Gallery of Art (NGA 13713)

article

encyclopedia article

drawing in the National Gallery of Art (NGA 15323)

article by Don D. Fowler et al published 1969 in Geological Survey Professional Paper

article

drawing in the National Gallery of Art (NGA 13836)

drawing in the National Gallery of Art (NGA 13160)

drawing in the National Gallery of Art (NGA 14868)

drawing in the National Gallery of Art (NGA 13375)

drawing in the National Gallery of Art (NGA 14794)

article

article

drawing in the National Gallery of Art (NGA 13132)

drawing in the National Gallery of Art (NGA 12413)

drawing in the National Gallery of Art (NGA 14799)

drawing in the National Gallery of Art (NGA 13038)

drawing in the National Gallery of Art (NGA 13664)