274 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



the central Coast Ranges of 7000 to 8000 feet of gray sandy shales, silts, 

 sandstones, and conglomerates. If it was not removed by erosion before 

 the Asuncion group was deposited, it rests on the erosion surface that 

 followed the Diablan orogeny. The Pacheco sediments may be less widely 

 distributed in the central Coast Ranges than the Asuncion but probably 

 more widely in the northern Coast Ranges (Taliaferro, 1943b). 



The Pacheco and Asuncion groups are separated by an unconformity 

 which in places in the central Coast Ranges is as angular as 80 degrees. 

 See Fig. 17.12. The disturbance represented by this unconformity has 

 been named the Santa Lucian by Taliaferro ( 1943b). Where the Asuncion 

 laps over older rocks than the Pacheco, which it does in a number of 

 places, it is difficult if not impossible to distinguish the two disturbances 

 — in fact, to recognize that more than one disturbance has occurred ( Tal- 

 iaferro, 1943b). 



The Santa Lucian orogeny was strongest in the Santa Lucia Range and 

 died out eastward. During the orogeny, the Gabilan mesa rose for the first 

 time (Taliaferro, 1944). This has been called the Diablo uplift by Reed 

 ( 1933 ) . Another land projection into the general north-south trough lay 

 to the south and has been called Catalina. At the north various authors 

 have recognized the Klamath Island or Klamathonia. All three are here 

 treated as peninsulas, branching off the volcanic archipelago, which as 

 a whole has been called Pacifica. See the tectonic map of the Late Cre- 

 taceous, Plate 12. 



As with other diastrophisms in California, the Santa Lucian appears to 

 have taken but a relatively short time. Although there was deep erosion 

 and widespread stripping, subsidence again took place, and the sea spread 

 rather rapidly over an area of considerable relief. The latest Upper Cre- 

 taceous, the Asuncion, is the most widespread Cretaceous unit in the Coast 

 Ranges. The Asuncion is predominantly coarse grained, being made up 

 of arkosic sandstone and coarse conglomerates perhaps 10,000 feet thick. 

 Fine sediments increase eastward. Franciscan debris increases toward the 

 west. Near the present coast, the basal conglomerates contain large angu- 

 lar to subrounded blocks of Franciscan chert, basalt, diabase, and sand- 

 stone, as well as well-rounded pebbles, cobbles, and boulders of the 

 ancient crystalline complex (Sur series and Santa Lucia granodiorite). 



To the east in what is now the great valley of California, the Upper 

 Cretaceous deposits have been divided into twelve foraminiferal zones, 

 and these grouped into seven stages (Goudkoff, 1945). During the first 

 three stages, the sea was transgressive eastward on the early Sierra Ne- 

 vadan landmass, and reached a maximum distance at the end of the third 

 stage except in the most northerly part. Near the end of the Upper Cre- 

 taceous (beginning of seventh stage) a low land barrier just south of 

 Stockton divided the region into two basins. The extent of the barrier 

 westward into the site of deposition of the Chico strata has not been 

 worked out. During the earlier stages, the sediments came from the west 

 as pointed out by Taliaferro, but in the later stages considerable material 

 came from the east according to Goudkoff, and some from the northwest. 

 The eastern source suggests slight uplift in the closing phase of the 

 Cretaceous in the Sierra Nevadan landmass. 



Evidence of igneous activity is present in many formations of the Meso- 

 zoic and Cenozoic in the central Coast Ranges of California, and Talia- 

 ferro, emphasizes the fact that volcanism was nearly continuous in one 

 place or another nearby during these eras. 



COLUMBIA SYSTEM 



Extent 



The term Columbia system will here be used to signify the mountains 

 and troughs of the Mesozoic era in British Columbia, southeastern Alaska, 

 the Yukon, Washington, western Idaho, and eastern Oregon. It is defined 

 approximately by the extent of the Triassic and Jurassic troughs and the 

 volcanic archipelago on the west that supplied much of the material to 

 the troughs. In many respects it is a parallel, if not a continuation, of the 

 great Sierra Nevada and Ancestral Coast Range systems of the United 

 States. See tectonic maps, Plates 10, 11, and 12, and Fig. 17.13. 



Triassic and Early Jurassic Phase 



In the southern interior of British Columbia and more particularly 

 southward from Kamloops Lake, strata, presumably of Triassic age, are 

 widely displayed. See map, Fig. 17.14. This assemblage is generally re- 



