106 



University of California Publications. 



[Geology 



rated from both Chico and Tejon by low marshes, so that no 

 actual contact could be observed. However, no marked irregu- 

 larity in the dip was seen. The strike of these beds was traced 

 to a point about three miles northwest of Benicia. Farther 

 than this no outcrops were seen which could definitely be called 

 Martinez. To the west of Benicia thick bedded sandstones closely 

 resembling those at Army Point were observed dipping steeply 

 to the northeast. Farther west the Chico again occurs, dipping 

 at the same angle as the thick bedded sandstones, but near the 

 shore it is folded and again dips to the southwest. The strike 

 and dip of these beds where carried across the straits are almost 

 identical with those south and west of Martinez. The most rea- 

 sonable conclusion would seem to be that there exists here a 

 closely folded syncline. 



Farther north, in Lake County, a similar structure seems to 

 exist, viz : a closely folded syncline having a general northwest- 

 southeast strike, with its apex about three miles northwest of the 

 town of Lower Lake. The width of the syncline below Lower Lake 

 is about three miles. The strata on both flanks dip at extremely 

 high angles toward the axis. The formations represented are, 

 Chico, Martinez and Tejon. The areal extent of the Martinez 

 outcrops was not determined, but they appear to be consider- 

 ably greater than those about the Strait of Karquines. Beds 

 of Martinez age may possibly be represented in northern Lake 

 County, near the town of Upper Lake. Dr. H. W. Fairbanks,* 

 who has examined that region, states that "a ridge of soft sand- 

 stone begins a mile northwest of Upper Lake and extends north- 

 westerly for about ten miles between Middle Creek and Bachelor 

 Valley. It rises perhaps one thousand feet above Clear Lake. 

 The strata are thick bedded and almost level, and are underlain 

 by the argillites of the older series which replace the sandstone 

 on the northwest. It contains no fossils, but from its resemblance 

 to the fossiliferous Chico-Tejon sandstones near Lower Lake, it 

 is judged to be of that period." When more detailed field map- 

 ping is carried out the Lake County beds will probably be found 

 to extend much farther to the southwest. 



*Geology of Tehama, Colusa, Lake and Napa Counties, Cal. State Min. 

 Bureau, 11th Ann. Kept., p. 62, 1891-92. 



