July 9, 1909] 



aCIENGE 



08 



Regular Program 

 Qeology of the Mexican Oil Fields: Mr. C. W. 



Hayes. 

 Qeology of the ilcKit trick- Sunset District, Cali- 

 fornia: Mr. H. R. Johnson. 

 The Temblor Range, along the northeast slopes 

 of which the McKittriek, Midway and Sunset oil 

 fields of California are located, includes, besides a 

 limited amount of granitic and metamorphic rocks 

 of pre-Cretaceous age, unaltered sedimentaries of 

 Cretaceous, Tertiary and Quaternary age. Briefly 

 the formations comprising the unaltered sedi- 

 mentary series are as follows: 



Knoxville-Chico {Cretaceous) Sandstone. — These 

 include between 7,000 and 12,000 feet of dark 

 green, well laminated and usually nodular shales 

 with intercalated sandstones which predominate 

 in the upper portion of the series. Some of the 

 sandstone includes zones of hard chocolate brown 

 nodules of considerable size, which give the beds 

 an appearance typical of the Cretaceous in the 

 region. The Cretaceous was probably deposited 

 upon an eroded surface of the pre-Cretaceous 

 metamorphic complex known as the Franciscan 

 formation in the Coast Ranges. 



Tejon Sandstone {Eocene). — This series of yel- 

 lowish brown somewhat nodular sandstone with a 

 small amount of intercalated clay shale reaches 

 a maximum thickness of about 2,500 feet. It 

 extends from the Devils Den and Antelope Valley 

 region southeast with considerable continuity 

 along the northeast flank of the range nearly to 

 Temblor Ranch. Although a non-conformity be- 

 tween the Tejon and Knoxville-Chico series is 

 known to exist, there is little field evidence of 

 this condition in the region. 



Wagonwheel Formation {Oligocenef) . — This is 

 a local occurrence of sandstones and several layers 

 of white diatomaceous shales which appear to be 

 of Oligocene age upon paleontologic evidence. If 

 this determination is correct it marks the first 

 discovery of marine Oligocene in the San Joaquin 

 Valley of California. The beds are located in the 

 isolated group of hills south of Bartons and north- 

 east of the Point of Rocks in the Devils Den 

 District. 



Vaqueros {Lower Miocene) Sandstone. — This is 

 a fairly continuous and usually easily recognizable 

 massive yellow sandstone including a couple of 

 fossiliferous reefs which, because of their superior 

 hardness, are easily traceable for long distances. 

 The formation is well distributed over the field 

 and is of variable thickness, its maximum prob- 

 ably being east of Annette, where over 2,000 feet 



has been measured. Elsewhere the formation is 

 less than 100 feet thick. 



Monterey {Lower Middle Miocene) Shales. — 

 Characteristic areas of this siliceous and calcare- 

 ous formation exist at a number of points in the 

 region. The largest of these areas occupies the 

 bulk of the Temblor Range from west of Temblor 

 Ranch southeast to the limit of the region studied. 

 It is exposed on either flank of the range for a 

 number of miles northwestward from this mass 

 and overlies the Vaqueros sandstone conformably. 

 The maximum thickness measured, in which, how- 

 ever, the beds may be doubled by close overturned 

 folding, is about 4,000 feet, a thickness consid- 

 erably less than the Monterey at other points in 

 the state. At the base of the Monterey there are 

 beds of sandstone transitional into the Vaqueros 

 and at several horizons in the formation similar 

 sandstone lenses occur. In a general way it may 

 be stated that the lower half of the Monterey in- 

 cludes a higher proportion of calcareous and 

 siliceous shales than the upper part, in which the 

 diatomaceous facies becomes more prominent. 



Santa Margarita Formation. — This formation 

 includes rocks of considerable variety, but along 

 the northeast flank of the Temblor Range heavily 

 bedded diatomaceous shales are characteristic of 

 it. While the formation rests unconformably upon 

 the Monterey there is little difl'erenee in dip 

 between the two series, and except for greater 

 hardness in the older and the predominance in 

 portions of the field of diatomaceous shale in the 

 younger formation, there is slight stratigraphic 

 basis for their separation. Southwest of Midway 

 the characteristic diatomaceous shales of the 

 Santa Margarita are intercalated with lenticular 

 beds of heavy granitic material which ofi'ers stri- 

 king contrast to the very fine organic shales with 

 which they are associated. The great diflference 

 in texture and origin of these two facies is in- 

 dicative of remarkable topographic or climatic 

 oscillations during the period of deposition of the 

 Santa Margarita, and presents an interesting 

 question for future solution. The total thickness 

 of the Santa Margarita is about 1,500 feet. 



Etchegoin-Jacalitos Formation. — This term has 

 been rather loosely applied in the field to a series 

 of clays, soft shales, gravels and loosely consoli- 

 dated sands which lies unconformably above the 

 Santa Margarita. It is of wide distribution 

 throughout the region and its uppermost beds are 

 the latest to have suffered deformation. Its thick- 

 ness is very variable but the maximum may be 

 stated as about 2,000 feet, although upon the 



