74 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



PENNSYLVANIAN 



Fig. 6.7. Thickness and paleogeographic map of the Pennsylvanian. 



the Humboldt Range, Nevada ( Nolan, 1943 ) . Northwestward into central 

 Idaho, it thins to about 4000 feet. See Figs. 6.8 and 6.13. 



In the Klamath Mountains the Nosoni formation occurs and is com- 

 posed of basaltic agglomerates, lithic crystal tuffs, flows of andesite and 

 of olivine basalt, dark brown, fossiliferous, shaly limestone, and dark 

 gray to brown tuffaceous shales and slates. The maximum thickness 

 measured by Hinds is 1200 feet. It is considered to be upper Lower 

 Permian (Wheeler, 1933). 



The Nosoni rests, probably unconformably (Hinds, 1939), on the Mc- 

 Cloud limestone which is highly fossiliferous. It was probably a massive 

 cherty limestone, but now owing to the Jurassic intrusions it is mostly 

 metamorphosed in various degrees to marble. It reaches a maximum 

 thickness of 2000 feet. Its fossils were first thought to represent a Penn- 

 sylvanian age, but a recent study by Wheeler ( Hinds, 1939 ) shows them 

 to be Lower Permian. 



The McCloud limestone overlies the Mississippian Baird formation dis- 

 conformably, so it appears that most of the Pennsylvanian was a time of 

 emergence. 



Central and Eastern Oregon. A heterogeneous group of east-west 

 trending ranges and dissected lava plateaus known collectively as the 

 Blue Mountains uplift or the Blue Mountains-Ochoco Mountains uplift 

 (Waters, 1933) extends from central to eastern Oregon. The ranges are 

 formed of Paleozoic and Mesozoic sediments and lavas and Mesozoic 

 plutons, and the complex protrudes island-fashion through the Columbia 

 River lava fields. The oldest beds that crop out are Lower Carboniferous 

 limestones and calcareous sandstones (Merriam and Berthiaume, 1943). 

 See Fig. 6.18. About 1000 feet of them are exposed, and they are called 

 the Coffee Creek formation. No volcanic materials have been noted. 



Overlying the Coffee Creek formation is the Spotted Ridge formation. 

 The exact contact relations have not been observed, but if an unconform- 

 ity does exist, it is probably not angular and does not represent much of a 

 time break. The Spotted Ridge consists of plant-bearing sandstones and 

 mudstones, conglomerates containing diorite, andesite, and dacite 

 boulders, and bedded chert. It may be 1500 feet thick. The plants are 

 believed to be Lower Pennsylvanian. 



