1078 



Subsurface Geologic Methods 



Many of the fields along the Gulf Coast are indicated by such slight 

 changes in gradient, and the outlining of structurally anomalous areas 

 becomes extremely difficult. Qualitative inspection of the map would 

 indicate that the large minimum axis must be caused by density variation 

 at great depth or by regional thickening of the mother salt bed, and that 

 the structural uplift is related to a salt uplift rising toward the surface. 

 Kettleman Hills-Lost Hills Trend, California — Figure 569 shows a 

 residual gravity map of a portion of the San Joaquin Valley, California. 

 Kettleman north dome is expressed by a gravity-maximum closure. 

 Towards the southeast a second gravity-maximum closure is encountered 

 which corresponds to Kettleman middle dome. The gradient again flattens 



Kettleman Hills 

 North Dome 



Indicotes top of structure 



Figure 569. Residual-gravity contours over structures in San Joaquin Valley, Cali- 

 fornia. Highest closing contour on each structure is indicated. (Adapted from 

 Boyd. Reproduced permission Geophysics.) 



