I would really love for the story of finding a cave in the Grand Canyon with Egyptian artifacts to be true. It's really an interesting story, and
who knows, maybe there is some truth it.
But whether or not the original story is true, the Google sites website linked in the OP seems to be a hoax. The photos didn't seem believable, so I
started doing some Google search by image searches. Here is the result...
The first alleged photo of Kincaid's cave is actually a picture of Stanton's Cave in the Grand Canyon taken by Shannon Kelly. You can see it here:
If you do a normal Google search on Stanton's Cave, you will see it is a well-known cave that seems unlikely to be the cave described in the original
early 20th century news story.
The second photo, alleged to be Powell's cave in the Grand Canyon, is actually a photo of a cave that is not even in the Grand Canyon. It's
apparently Helme Cave in Estonia. You can see it here: Source
The alleged shrine in Powell's Cave is also not in the Grand Canyon, it's in India. It's a Buddha statue in Mumbai. You can see it here:
The photo of the alleged gold tablet is actually one of the artifacts allegedly found by John Brewer in a cave in central Utah. Those artifacts
apparently caused something of a stir among Mormons in Utah, but they don't seem to have been found in the Grand Canyon. And they are questionable
too... apparently the LDS church considers them a hoax. Source
The photo of the alleged unfinished Egyptian pyramid in the Grand Canyon is apparently actually a photo of a mountain in Death Valley that was mined
by the vat leaching process: Source
Not sure about the other photos at the Google sites website linked in the OP, but it looks like someone took a lot of photos from a wide variety of
other places and wove them together with the legend and some creative fiction to build a hoax site. Or maybe they copied it all from others who did
Still, the legend is interesting enough that it seems worth searching for the cave from the original early 20th century news story.