1368 EDWARD D. LYNTON 
2. The North dome shows low intensity along its axis surrounded 
by high intensities on the flanks over eroded edges of magnetic beds. 
3. The Middle dome shows high intensity at the axis, as would be 
expected from a magnetic bed arched continuously across the structure 
and not eroded. The obvious inference is that the Middle dome is 
structurally lower than the North dome. 
4. The magnetically active horizon has been identified as the 
vivianitic sandstone of the upper Etchegoin (McKittrick group) of 
Pliocene age. 
5. It has been discovered that this sandstone is also strongly polar- 
ized along definite lines. 
SOUTH DOME-LOST HILLS STRUCTURE 
The area surveyed is a strip extending northwest-southeast from the 
northern end of the Lost Hills oil field, Kern County, to and including 
South dome of Kettleman Hills, Kings County, on the western side of the 
San Joaquin Valley, California. It ranges from 2 to 4 miles in width 
and has a length of 14 miles. 
The country covered by the survey is one of relatively small relief. 
The central part is a gently rolling, alluvium-covered plain, slightly 
sloping downward toward the northeast. At either end of the area are 
low, rolling hills rising from 50 to 200 feet above the general level of the 
country. The Lost Hills, from the west side, appear as the crest of a 
gradually rising plain, but on their eastern side they rise more abruptly 
and are more prominent features of the landscape. 
The only formations exposed are Etchegoin (Pliocene), San Joaquin 
clays and Tulare (Upper Pliocene), and alluvium. 
The folding in the Lost Hills-South dome district is a segment of 
the long, anticlinal fold, extending northwest-southeast for 60 miles. 
Folding along this line has also caused the North and Middle domes of 
Kettleman Hills and the Coalinga anticline. Recurrent movements 
along the line have occurred since its probable beginning, at the end of 
Cretaceous time. Gentle folding was repeated at the end of the Eocene. 
More intense folding recurred at the close of Miocene and Pliocene time. 
Surface evidence of the structure is incomplete, because of the 
mantle of alluvium in the central part of the area. The topographic 
“high” and surface exposures show the anticlinal origin of the Lost 
Hills. The trend of the Mulinea bed, at the top of the Etchegoin, and 
the dips obtainable at the South dome, disclose the northwestward 
plunge at that point. 
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