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A large mid-Eocene channel is evident near Yoakum, Texas, from a study of the electrical logs of more than 50 wells. The channel, clearly erosional, is filled largely with silty shale, in sharp contrast to the sandy continental character of the typical Wilcox strata through which it was gouged.

This channel or canyon can be traced for more than 50 miles, from its mouth near the southeast line of Lavaca County updip north-northwesterly to the outcrop of the Wilcox in Bastrop County. At its maximum development, near the town of Yoakum, it has a width of 10 miles and a depth of approximately 3,000 feet.

A completely satisfactory explanation of the origin is difficult. The factors involved must include the following.

1. The presence of a major stream.

2. The great thickening of the Wilcox now known to exist, to as much as 8,000 feet at the outer edge of the former shelf, which placed an unstable mass of sediments adjacent to deep water.

3. Slumps and slides at the mouth of the large stream, triggered by fault movement and extended inland by stoping guided by the stream channel, created turbidity currents powerful enough to cut a gentle gradient to the sea bottom.

4. An abrupt, brief transgression of the sea resulted in rapid filling of the channel and deposition of a blanket of shale over a large area outside the channel. This was followed by a regression during which the extraordinarily thick and extensive sands of the Carrizo were deposited. These clean massive sands of the uppermost Wilcox entirely obliterated any evidence of the great channel below.

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