Treaty of Guadalupe-Hidalgo Land Claims Act of 2018 This bill establishes the Treaty of Guadalupe Hidalgo Land Grant-Merced Claims Commission to conduct a hearing on each qualifying petition that shows the claimed boundaries of a land grant-merced. A "land grant-merced" is a specified community land grant, or a community, village, town, or settlement, the land of which was granted by Spain or Mexico between 1689 and 1854 within the Territory of New Mexico, which now includes New Mexico, Colorado, and Arizona, to the community, village, town, or pueblo, or to a person to found or establish a community, village, town, or settlement. After a hearing, the Commission may recommend as restitution any one of the following possible restitutions: convey federal land; grant stewardship rights to all or part of federal land; grant priority access and use rights to such lands for the harvesting of natural resources, such as timber and minerals, grazing and watering of livestock, or hunting and fishing; grant priority rights to leases, special use permits, and easements on federal land, to acquire federal lands that may become available for disposal, or to obtain new, unused, or unrenewed grazing allotments on federal lands. The bill prohibits the impairment of the rights of any acequia located on federal land as the result of enactment of this bill, including the right to the use of water by valid water right owners and access to the acequia for maintenance and improvements to its easement and infrastructure.