Theories for the Formation of Grand Canyon Sidebar 3

The Precocious Gully Theory

Figure 3 Figure 4 Figure 5

The Precocious Gully Theory states that the upstream drainage basin is ancient, but the Grand Canyon segment of the river is relatively young. This theory says that the Kaibab Monocline formed 50-70 million years ago (mya). Over 10 million years ago (before the Grand Canyon was eroded) the Colorado River flowed south from Utah east of the Grand Canyon area, and turned southeast through the Little Colorado River (Figure 3). Westward drainage over the Kaibab Monocline resulted in the erosion of a gully that eventually joined with the Colorado River (Figure 4). The Colorado River was gradually diverted from its course through the Little Colorado River to cut through the Kaibab Upwarp and erode the Grand Canyon (Figure 5).

Problems with the Precocious Gully Theory:
There are four main problems with the Precocious Gully Theory.

First, there is no evidence that the theory would even work. "There are many elevated plateaus in the world, but very few of them have Grand Canyon sized gullies through them" (Austin, 1994 p.90). There is no reason why the river would have naturally cut where the Grand Canyon is. There are several major structural elements of the area (fault zones, etc.), but they all run north-south, and the Canyon is east-west. There is also no zone-of-rock weakness or trough-like sag in the plateau to guide the gully formation.

The second problem is that the evolutionary dates assigned to rock layers in related areas do not agree with the theory. Potassium-Argon dating methods at the west end of the Canyon have determined that the Grand Canyon was eroded between 5.0 and 3.8 million years ago. However, the estuary delta region of the Colorado River north of the Gulf of California gave an "age" of 5.3 million years. Further, Potassium-Argon dating determined that the Little Colorado River formed between 4.2 and 2.4 million years ago. These three dates have several contradictions. First, the "age" of the river at the delta is older than the maximum age for the establishment of the Colorado River through the Grand Canyon region. Second, the time between the formation of the Little Colorado Riverbed (4.2 mya) and the Colorado Riverbed (3.8 mya) "requires that the erosion of the Grand Canyon along with the Little Colorado River drainage occurred in just a fraction of a million years!" (Austin, 1994).

The third problem with the theory is that it requires the Kaibab plateau to be 70 million years old, with no significant erosion occurring all that time.

The fourth problem with the theory is that there is "no abandoned channel for the postulated ancestral Colorado River… (either) southeast or northeast of the Grand Canyon." (Austin, 1994). The Precocious Gully Theory is filled with problems, and is thoroughly lacking in evidence.

References
Austin, S.A. 1994. "How was the Grand Canyon Formed?" in The Grand Canyon: Monument to the Flood Institute for Creation Research, Santee. p. 83-110.

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