Abstract

Five slump faults along the rim of the Markley Gorge are identified in this paper; it is likely that many others exist. Slump faults have not been identified along the rims of the other gorges in the Sacramento Valley but their presence can not be ruled out.

Identification of these slump faults is totally dependent upon subsurface well control and resulting structural interpretation because the gorge has only limited surface exposure. Each of the identified faults intersects a well within 600 feet of the base of the gorge and appears to flatten with depth. The amount of section cut out ranges between 160 and 480 feet.

Because most of these faults intersect only a single well, their recognition as slump faults adds an element of uncertainty involving faulted wells near the rim of the Markley Gorge. Are some of our structural interpretations erroneous because a slump fault has not been recognized as such? Any fault near the rim of the Markley Gorge should be viewed with suspicion when the following circumstances are present.

1. The fault is not identifiable in more than one well.

2. All other reasonable structural interpretations can be eliminated.

3. The position and limitations imposed by surrounding wells allow for a slump fault interpretation.