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A detailed study has been made of several outcrops of late Precambrian-Early Cambrian strata in the southern Kelso Mountains. These strata, which are part of the predominantly detrital basal sequence of the Cordilleran miogeocline, previously have been described only in reconnaissance.
In the Kelso Mountains, these strata have been assigned to 5 regionally recognized formations. The late Precambrian Johnnie Formation, which lies unconformably on metamorphic basement, displays rapid lateral changes in lithology and thickness, perhaps due in part to infilling of uneven basement topography. Of 4 sections of Johnnie exposed, 3 are similar, consisting of 91-141 ft of quartzite and dolomite. Conformably overlying the Johnnie Formation are the late Precambrian Stirling Quartzite (186 ft thick, only the uppermost regional member is present), the late Precambrian-Early Cambrian Wood Canyon Formation (712 ft thick), the Early Cambrian Zabriskie Quartzite (75 ft thick), and the Early Cambrian lower part of the Carrara Formation (70 ft thick).
Comparison of these strata with equivalent miogeoclinal strata in the Providence Mountains 8 mi southeast and with Early Cambrian cratonic strata in the Marble Mountains 30 mi south shows that the northeast-trending craton-miogeocline boundary was not an abrupt break (an interpretation based on comparison in Nevada and Utah of thick allochthonous miogeoclinal strata with autochthonous cratonic strata), but rather a relatively broad transition zone of gradual thickening of strata from southeast to northwest.
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