Picture this: An elaborate, expensive tramway is built across the Grand Canyon, allowing a rare resource to be harvested from a remote cave below the North Rim. The resource? A nitrogen-rich animal byproduct: guano. Today, the idea sounds bat-dung crazy. But in the mid-20th century, when this ambitious scheme unfolded (and then folded), guano was highly sought for use as fertilizer. So, after the cave was discovered 650 feet above the Colorado River in the 1930s, attempts to harvest the guano began.

None was successful, however, until the U.S. Guano Corp. came along in the mid-1950s. In 1957, the Associated Press reported that prehistoric “man-sized carnivorous bats” — in reality, Mexican free-tailed bats, which are common in Arizona — had deposited what a company engineer estimated was 100,000 tons of guano in the cave. But the location posed an extreme challenge. The company’s solution was to string a tramway cable more than 8,000 feet from the cave to a point on the South Rim, across the river. The guano would be vacuumed out of the cave, loaded into a cable car and carried up the tramway to the rim before being trucked to Kingman and prepared for distribution.

Cable failures and other mishaps plagued the project, and according to an article in The Journal of Arizona History, the cost of the tramway ballooned to $1 million. But that seemed a prudent investment for an estimated $15 million — the equivalent of about $150 million today — in guano. And initially, the venture appeared to be succeeding: Newspapers soon featured ads touting Grand Canyon bat guano, sold in 3-pound packs for 59 cents, as “nature’s perfect plant food.” And the tramway was used for the climactic scene in a movie, 1959’s Edge of Eternity.

But once crews moved deeper into the cave, they found it far less full of dung than expected, and miners ended up collecting only about 1,000 tons of guano before the mine shut down around 1960. Not long after that, a military aircraft severed the tramway cable. U.S. Guano received some compensation from the federal government but was liquidated soon thereafter, with the company dubiously citing competition from guano importers. In all, the operation had cost about $3.5 million — far more than the value of the extracted guano.

Today, the most obvious reminder of the project is the tramway head house, which is at Grand Canyon West, the Hualapai Tribe’s development on the South Rim. You’ll find it at an overlook with an appropriate name: Guano Point.