-- "Explorations in Grand Canyon," Phoenix Arizona Gazette (April 5, 1909)
An expedition under the "S.A. Jordan" (another figure whose existence is difficult to verify) started mapping the cavern in good adventurer-style. Highlights include two large chambers, radiating passages, assorted idols, mummies wrapped in bark, mysterious hieroglyphics, and a "grey metal" that baffled scientists, but resembles that most valauble of D&D coinage metals, platinum. And one other intriguing random treasure: "Strewn promiscuously over the floor everywhere are what people call "cats eyes', a yellow stone of no great value. Each one is engraved with the head of the Malay type." The whole 1909 article is helpfully provided here, rich with cool detail.
Even better, Jack Andrews, a researcher on the topic, offers a map in the article on his website:
Admittedly, The layout's a little plain as dungeons go, but a location that can only be reached by climbing nearly 1500 feet down the wall of a deep gorge, or up from a fast moving river, is actually the sort of place adventurers ought to be going. Probably there'd be some nonhuman inhabitants in a fantasy game, but cranky mummies or even rival treasure-hunters would work in a pulp setting or wild west.
I wonder what those "cat's eyes" stones will appraise for?