The least visited national monument in the West (second in the whole US only to Aniakchak in Alaska) is Alibates Flint Quarries
, which occupies a small area of grassy limestone plateaus and valleys on the southeast side of Lake Meredith, all of which is part of a much busier NPS preserve (Lake Meredith NRA
). The purpose of the monument is to preserve the site of several ancient flint quarries, thought to have been in use for some 12,000 years. Despite their historical importance, the quarries now are just minor, overgrown depressions, unremarkable to look at, and they may only be visited on ranger-led tours, which have to be reserved in advance.
Alibates Flint Quarries - full description