74 University of Washington Publications in Geology [Vol. 1 



with a very low dip to the northeast. They are apparently unconformable upon 

 the marine Tejon sediments which occur only 1,500 feet to the south. These 

 beds were probably deposited contemporaneously with those at Lincoln Creek. 



About five miles to the southeast of Winlock, along the south bank of Cowlitz 

 River, there are exposures of Oligocene strata. At this locality there is a cliff 

 exposed for about fifteen feet above the water's edge. The lower five feet of 

 this section is composed of a coarse-grained gritty to pebbly, massive, brown- 

 colored, iron-stained sandstone, which lies nearly horizontal with a very low dip 

 to the northeast. These rocks contain a rich marine molluscan fauna. The upper 

 portion of this section grades into a conglomerate in which the pebbles range in 

 size up to four inches in diameter. They have been derived largely from basalt. 

 The upper beds are also fossiliferous. Exposures of marine Oligocene strata have 

 not as yet been recognized southeast of Cowlitz River. The region is heavily 

 covered with deposits of glacial drift or river wash. The Oligocene deposits at the 

 Greece ranch on Cowlitz River were probably deposited during early Oligocene 

 time near the south end of the Chehalis Valley embayment and in proximity to the 

 mouth of some Oligocene river. 



