If Dr. Walt Brown's hydroplate theory is correct, and the Grand Canyon is a result of the rapid release of millions of tons of water that had been trapped in two massive inland seas (Grand Lake and Hopi Lake, shown in the image on this page of the online version of his book), then the release of so much water should have left evidence all the way along its path to the ocean.  The evidence of such an event would look very different than the evidence that we would find if the Grand Canyon was carved slowly over tens of millions of years by the action of the Colorado River (the conventional explanation).  

The previous discussion presented just that kind of evidence, in the form of six thousand cubic miles of sediments along the northern basin of the Gulf of California.  However, diving down to the floor of the Gulf of California is not an easy undertaking.  Fortunately, we should expect to find plenty more evidence in between the Grand Canyon and the Gulf of California which could provide clues as to the mechanism behind the Canyon's formation -- evidence that would look very different depending on whether its formation was caused by massive amounts of water moving at very high velocity after huge lakes breached, or whether its formation was instead caused by a relatively small river moving at normal speeds over millions of years.

The image above, from Google Maps, shows the distinctive terrain between the two features (Grand Canyon and Gulf of California), a desert region resembling a vast flood plain, marked by ridge line features that resemble lines of dirt left over by a drainage event.  This area is part of the larger "Great Basin" region, and contains the Mojave Desert.  If you can imagine lining the bottom of a bathtub with dirt, then filling it up with water, and then blowing a hole in the side of the bathtub with a large firecracker (like an M-80) [don't try this at home -- this is only a thought experiment], you might be left with a similar pattern of dirt "eddies" along the floor of the bathroom after all the water flowed out of the tub and out of the bathroom (assuming the water had someplace lower to run towards).

If you explore the terrain shown above in person (and I have spent quite a bit of time crawling around in the regions shown in the map) you will find that it is full of very interesting terrain, and that most of the ridge line features that rise up out of the desert are full of a mix of rocks and boulders of all sizes and shapes.  Some of these have been rounded into spheroid shapes by some process.  According to Dr. Brown's interpretation of this evidence, these provide further support for the hypothesis that the Grand Canyon was the product of massive volumes of high-velocity water, which removed thousands of cubic miles of sediments and flowed towards the Gulf of California like a massive tsunami.  

In figure 136, which is found on this page of Dr. Brown's chapter on the Grand Canyon (under paragraph 13, "Missing Dirt"), he presents a photograph of two such spheroid boulders, located south of Bullhead City, Arizona about a mile east of the Colorado River and a hundred feet in elevation above that river (see image below).  The approximate location of this photograph is marked in the map above with a red arrow.  

What could have rounded these boulders into their smooth shapes?  One possibility is the action of high-velocity water, moving them along the bottom for miles at a rapid pace, and depositing them far from the present river and at an elevation high above it.

These boulders shown in Dr. Brown's book (the same image can be seen in the hardcopy version of his book, on page 205 of the 8th edition) are by no means anomalous to the region.  Other similarly rounded boulders can be seen in the Coachella Valley, far to the west and south of the red arrow in the image above, but still in the area that would have been flooded by the rapidly-moving water from the breaching of Grand and Hopi Lakes, if the hydroplate theory is correct.  See for example the photograph at the top of this page (linked) showing very spheroid boulders, some piled on top of one another with large gaps in between them.

There are a few possibilities for explaining the boulders in that image, which are located in Joshua Tree National Park at the approximate location of the marker (the red marker, with the letter "A" on it) in the image below:

That location can be found on the map at the top of this post as well -- it is just north of the Salton Sea and Interstate 10 (you can find the Salton Sea on the map at the top of this post -- it is about center from the left and right sides of the image, but closer to the lower edge of the image).

Those boulders could have been carved into spheroid shapes by the wind, although this explanation seems somewhat unlikely (especially as they are piled on top of one another -- the wind would not be expected to deposit large boulders on top of one another in that manner).  They could have been ejected from an ancient volcano in this spheroid shape and left in a pile as shown in the photograph (while this possibility does not seem to be the correct one, especially given the composition of the rocks themselves, it is a possible explanation).  Or, they could have been eroded into a spheroid shape by rolling for miles at the bottom of a huge flow of water, and left in the location we find them today by that water as it coursed down through the maze of mountainous terrain features towards the Gulf of California.

In his discussion of the evidence (again from paragraph 13 on this page of his online book), Dr. Brown writes:

At least 2,000 cubic miles of Mesozoic sediments were stripped off the layers surrounding and above what is now the Grand Canyon. Only then could the 800 cubic miles of sediments be removed from inside the Grand Canyon. All that dirt was spread downstream from the Grand Canyon, primarily into the northernmost 220 miles of the Gulf of California.
Relatively few sediments were deposited along the Colorado River as it flows south toward the Gulf of California. Rounded boulders mixed with sand and clay are often seen where today’s side streams have cut channels 100–200 feet deep. Those rounded boulders show that they were tumbled and transported by high-velocity water. Unsorted mixtures of sand, clay, and boulders show that the turbulent, muddy water suddenly slowed, depositing the unsorted mixture. [See Figures 136 and 137.]

Clearly, if the Canyon were carved by the normal action of the Colorado River over millions of years, we would have to find another explanation for the location and condition of these boulders.  It would be difficult (if not impossible) to explain this evidence by saying that the river has been flowing at a fairly uniform rate and volume for millions of years.

If you read further in paragraph 13 on the web page cited above from Dr. Brown's book, you will find a reference to a recent (2011) study of the very area under discussion, which looked at the geology of the area shown in the map above and said that although the sediments in the area in question have been widely studied for over a hundred fifty years, "their origin remains unresolved and their stratigraphic context has been confused" (Stratigraphy and Depositional Environments of the Upper Pleistocene Chemehuevi Formation along the Lower Colorado River, Malmon, Howard, House, Lundstrom, Pearthree, Sarna-Wojcicki, Wan and Wahl, 2012 -- link to full report).

They offer a new theory for the origin of the sediments in the vast flood plain between the Grand Canyon and the Gulf of California, namely "a single major episode of fluvial aggradation, during which the Colorado River filled its valley with a great volume of dominantly sand-sized sediment."

While it is nice to see conventional geologists arguing for an extraordinary event to explain evidence that clearly calls for such an explanation (and note that their study was published long after Dr. Brown wrote the discussion quoted above, which can be found in his 2008 hard-copy 8th edition, minus the reference to the 2011 study), their explanation still fails to explain the rounded boulders shown in the two locations discussed above.  A flooding river might move large rocks, but it would not be expected to have the velocity to roll them along for miles at high speeds and round them into spheroids, nor would it be able to pile them up in the jumble shown in the Joshua Tree image.

In short, the evidence on the ground in between the Grand Canyon and the Gulf of California appears to support the hydroplate theory, and to refute the conventional explanations.  And that is in addition to the tons of sediments at the bottom of the Gulf of California (which suggest a rapid high-volume dumping, because if those sediments were deposited by a river over millions of years, it would have been expected to build up a large river delta, which is not present at the north end of the Gulf, as discussed in the previous post and in Dr. Brown's books).

All of this evidence can be added to the massive amounts of evidence in the vicinity of the Grand Canyon itself, which suggests that this incredible terrain feature is the product of a catastrophic event involving huge volumes of high-velocity water, and not the action of a normal river moving with normal volumes and normal velocities over the course of millions of years.  And yet teachers in school responsible for the education of children from the youngest grades through graduate school, as well as all the guides at the Grand Canyon itself, continue to insist on presenting the conventional theory as if it were settled fact, and as if anyone suggesting an alternative explanation is way out of bounds.