Geology . Fig. 560.—A floated crag of scoria, in recent lava-flows, Cinder Buttes, Ida. (Russell, U. S. Geol. Surv.) nary period, but there are in numerous places igneous rocks which areclearly post-Tertiary, some of them even late Quaternary. Some ofthese very young igneous rocks have been referred to in connectionwith the history of Lakes Bonneville, Lahontan, and Mono, but theyare by no means confined to the basns of these lakes. Mount Shastashows several post-glacial lava-flows,2 and there are small cindercones on alluvial cones at the east base of the Sierras in southeasternCalifornia. 1
Geology . Fig. 560.—A floated crag of scoria, in recent lava-flows, Cinder Buttes, Ida. (Russell, U. S. Geol. Surv.) nary period, but there are in numerous places igneous rocks which areclearly post-Tertiary, some of them even late Quaternary. Some ofthese very young igneous rocks have been referred to in connectionwith the history of Lakes Bonneville, Lahontan, and Mono, but theyare by no means confined to the basns of these lakes. Mount Shastashows several post-glacial lava-flows,2 and there are small cindercones on alluvial cones at the east base of the Sierras in southeasternCalifornia. 1 Fairbanks, Jour, of Geol., Vol. VI, p. 566. 2Diller. Physiography of the United States, pp. 245 et seq. •ITS GEOLOGY In other localities, the reference of lavas, tuffs, etc., to this perioddepends on different criteria. In southern California (Mohave desert). Fig. 561.—Oven of clots of plastic lava. Jordan Craters, Ore.(Russell, U. S. GeoL Surv.) and northern Arizona (vicinity of Flagstaff), for example, there arecinder cones and lava-flows of limited extent which are so slightly
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