Christopherson, Robert W. Geosystems : an introduction to physical geography / Robert W. Christopherson. - New York : Macmillan, c1992. - xii, 616, [47] p. : col. ill., col. maps ; 26 cm. ISBN: 0023224436 LCCN: 2009379462 LC Class. No.: GB54.5 .C48 1992 / .C48 1992