98 WARREN DUPRE SMITH AND EARL L. PACKARD 



the base of the Columbia lavas at Eagle Creek, Multnomah County. 

 This formation consists of hardened ashy clay and has yielded a 

 flora of over forty species, which is thought to be of upper Miocene 

 age. Such a determination would place the Columbia lava in the 

 late Miocene, or Pliocene, which is contrary to the evidence afforded 

 by the Mascall fauna, which occurs within the John Day Valley 

 and has yielded an extensive middle Miocene fauna. 



Unfortunately this name is preoccupied by the Triassic Eagle 

 Creek beds of the Wallowa Mountains. The Miocene formation 

 might well be called the Warrendale formation, from the town of 

 that name, near Eagle Creek, a tributary of the Columbia. 



W. D. Smith' has described a series of at least four hundred feet 

 of buff-colored tuffs occurring on the Santiam River near Cascadia, 

 which may be correlated with the Warrendale formation, or pos- 

 sibly with the John Day. As yet no fossil remains have been found 

 in these tuffs. 



Lying above the Warrendale formation, which may later prove 

 but a local interbedded deposit, is the Columbia lava, a name 

 applied by Russell to basaltic flows occurring extensively in eastern 

 Washington and redefined by Merriam^ to include only the lavas 

 younger than the John Day Ohgocene and older than the Mascall 

 middle Miocene. As thus defined the Columbia lava is a wide- 

 spread formation covering large areas in eastern Oregon, eastern 

 Washington, western Idaho, and northern California, entering 

 into the structure of the Oregon Cascades as shown by Diller, 

 Williams, and Smith, and occurring presumably in discontinuous 

 areas of western Oregon. 



The Columbia lava series consists of basaltic flows, often inter- 

 bedded with lateritic deposits and tuffs. These vary considerably 

 from place to place as regards number and thickness. Twenty- 

 three have been counted on the John Day and twenty in the 

 Columbia gorge. 



East of the Cascades these flows are often but comparatively 

 little deformed, though in places they have been faulted, resulting 

 in the typical block-fault t3rpe of mountains. In some places this 



^ W. D. Smith, Univ. of Oregon Bull. i6, p. 38. 

 ^J. C. Merriam, op. cit., II, 304. 



