The letter you need is required by federal or state law. Under these laws, each federal and state agency (or any agency using federal funds) is required to “take into account” cultural resources in its projects and activities.
“Taking into account” cultural resources--like historic structures or archaeological sites-- requires specific steps. Read an overview of the process (on the Advisory Council on Historic Preservation website).
After you have made a determination about cultural resources, you must give the State Historic Preservation Office (SHPO) the opportunity to comment. This comment letter is the letter you need.
Get more specifics on requirements for projects that may affect historic sites.
Get more specifics on requirements for projects that may affect archaeological resources.