"Mining for guano and tourism have had some effects on the integrity of some of the 81 caves found in CCNP. During the period 1903-1923 an estimated 100,000 tons of bat guano was removed by hand tools from the entrance areas of the accessible caves" (AB Eval)

"In 1890, Laysan was leased by the Hawaiian Kingdom to the North Pacific Phosphate and Fertilizer Company for a period of 20 years. Guano mining and digging occurred on Laysan from 1892 to 1904. This period saw the construction of several buildings, including a lighthouse and a small railroad, which supported this trade; between 100 and 125 tons of guano could be shipped from Laysan per day" Nomin file.
See www.papahanaumokuakea.gov

"Local communities continue to observe a centuries-long tradition of molong, “take only what you need”, when harvesting guano and highly valuable edible bird’s nests from the caves complex." (AB ev)

Bat Cave Mine was the site of significant investment to extract guano commercially in the 1950s - but small volumes and low price made the project unsuccessful. The mine is on the north side of the Colorado river and became a part of the National Park in 1974 (pre-inscription). An aerial ropeway was built to take the guano to the south rim within the Hualapai Indian Reservation at "Guano Point" (outside the NP).
See www.grandcanyonwest.com