Casa Grande Ruins National Monument Boundary Modification Act of 2013 - Authorizes the Secretary of the Interior to transfer or acquire only from willing sellers the private or state lands or interests identified on the map entitled "Proposed Casa Grande Ruins Boundary Modification".

Transfers administrative jurisdiction of specified withdrawn federal lands administered by the Bureau of Land Management (BLM) or the Bureau of Indian Affairs (BIA) to the National Park Service (NPS).

Transfers to the BIA the administrative jurisdiction of certain federal land administered by the NPS for purposes of the San Carlos Irrigation Project.

Requires the Secretary to administer all such transferred or acquired lands as part of the Casa Grande Ruins National Monument in Arizona.

Requires the Secretary, as consideration for the acquisition of state and private lands, unless such lands are donated, to: (1) pay fair market value for such lands; and (2) convey to the state of Arizona and private land owners, as the case may be, federal lands, interest in federal land, or any other federal asset of equal value located in Arizona.

Authorizes the Secretary to enter into an agreement with the state of Arizona to provide for cooperative management of specified state trust lands.