130 University of California Publications in Geology [Vol. 10 



OCCUBRENCE AND AGE 



The Ironside region, in which the mammalian finds are reported, 

 is situated on the extreme northern border of Malheur County, Oregon, 

 and is about thirty miles west of the middle of the eastern border of 

 the state. This region lies at the southeastern base of the Blue Moun- 

 tains, and is at the northern end of the great series of broken plains 

 and short mountain ranges extending through southeastern Oregon 

 into Nevada. The Ironside region is drained by AA 7 illow Creek, a 

 tributary of Malheur River. 



The beds in which the fossil remains were found by Mr. Anthony 

 are in the immediate vicinity of Ironside Post Office. Some of the 

 exposures are at an elevation of 3800 feet above sea-level. Somewhat 

 to the east of Ironside similar sedimentary formations seem to be 

 situated at an elevation of at least 4000 feet. 



The mammal- bearing formation consists of buff sandy shales and 

 shales with but little sand. The beds stand at varying angles ranging 

 up to a degree of inclination of at least 20 degrees. 



Locality 3037. at which the most important specimens were found, 

 is located about three-fourths of a mile southwest of Ironside Post 

 Office. At this locality, Mr. Anthony secured several fragments of 

 upper teeth of Hipparion, a well-preserved lower tooth constituting 

 the type of Hipparion anthonyi, a fragment of a rhinoceros tooth, and 

 fragments of mastodontine teeth. One quarter of a mile south of 

 locality 3037 Elmer Molthan obtained a well-preserved tooth of a 

 mastodontine form apparently derived from beds not widely different 

 in age from those at locality 3037. 



The equid remains found in the sediments near Ironside represent 

 a form most closely approaching in stage of evolution the Hipparion 

 species from the Ricardo Pliocene. The stage of evolution of the 

 fragmentary equid remains from Ironside is approximately that of 

 the Hipparion species known from formations of the Great Basin and 

 Pacific Coast provinces generally referred to the Pliocene. There is 

 good reason for believing that the sediments at Ironside are not 

 younger than middle Pliocene and not older than late Miocene. Future 

 investigations should bring out more exactly the age relation of this 

 formation to the Rattlesnake Pliocene of the John Day Valley. The 

 fauna listed from the Idaho formation by Lindgren 1 in his important 

 papers on the Tertiary formations of southwestern Idaho contains as 

 one of its important elements equid forms which have been referred 

 i Lindgren, W., 20th Ann. Rep. U. S. Geol. Surv., Part 3, p. 99, 1900. 



