88 University of California Publications in Geology [Vol. 10 



South America before TJrsus crossed from the Old World. If this 

 view expresses the history of migration of bears in America, remains 

 of Arctotherium, or of a type ancestral to this genus, might be expected 

 in earliest Pleistocene or Pliocene deposits of North America. The 

 absence of Arctotherium and of well authenticated remains of near 

 relatives of this division of the bear group from North American 

 deposits older than those containing Ursus has sometimes been inter- 

 preted to indicate the migration of Arctotherium, or of its ancestors, 

 to South America by some route other than that through North 

 America. 



In the course of a special study of the later Tertiary deposits of 

 eastern Oregon carried on by the Department of Palaeontology of 

 the University of California in the summer of 3 016, remains of a 

 member of the bear group were discovered by Chester Stock and 

 Clarence L. Moody in beds of the Rattlesnake Pliocene of the John 

 Day region. The significance of this discovery, especially with rela- 

 tion to other studies on correlation and migration of Tertiary mammal 

 faunas, makes desirable a statement of the evidence in advance of a 

 full report on the Rattlesnake fauna. 



OCCURRENCE 



Remains of the Pliocene bear (no. 22362) were found in the Rattle- 

 snake formation exposed on the East Fork of the John Day River 

 in northeastern Oregon. The locality is situated near the center of 

 N.W. 14 sec. 30, T. 12 S.. R. 26 B. v Willamette Base Line and 

 Meridian, Grant County. Oregon, approximately five and one-half 

 miles west of Dayville, and not over three-fourths of a mile south 

 of the type section of the Rattlesnake formation. The specimen was 

 found on a low ridge between Rattlesnake Creek and Little Rattle- 

 snake Creek. 



In the typical area the Rattlesnake formation is tilted at an angle 

 of approximately five degrees and rests upon a basement formed 

 by sharply deformed, truncated strata of the Mascall Middle Miocene. 

 The present canyon of the John Day River cuts through the basin 

 of accumulation of the Rattlesnake." In the bottom of this canyon 

 Pleistocene mammal remains are found in terrace deposits laid down 

 after the canyon had attained approximately its present form. The 

 stage of the Rattlesnake is thus limited on one side by antecedent 

 Middle Miocene and by the period of deformation and extensive erosion 

 intervening between deposition of the Mascall and beginning accumu- 



