On occasion, transportation projects encounter potential historic landscapes of unusual size. Very large landscapes, thousands of acres or more, present special challenges to both cultural staff and management. The identification and formal evaluation of a large historic landscape can be time consuming and costly, often controversial, but may be necessary. For example, a reclamation district landscape is likely to encompass the entire district, no matter how large. No useful purpose is served, however, by identifying an entire region, such as the Great Basin or Southern California, even if a logical argument can be constructed. As a general rule, it is preferable to identify a reasonably defensible smaller landscape rather than stretching boundaries to distant horizons, and perhaps threatening the credibility of the process.

When a very large landscape has been found, the responsible federal agency and the SHPO may be consulted, either informally or through an agreement document, on options that would allow compliance without unreasonable expenditure of effort. It may be possible, if the agency and the SHPO agree, to conduct an abbreviated survey focused on the identification and evaluation of involved individual landscape components, with summary documentation of the landscape as a whole. When a project involves only a narrow corridor or individual components that can be clearly documented as either contributing or noncontributing, a landscape could be treated as eligible for the purpose of the project without undertaking a full study. However, it is often worthwhile to undertake a full formal evaluation in order to establish landscape boundaries and contributors, especially when the landscape can be expected to be encountered in future projects. In all cases, decisions should reflect an understanding of the property’s historic values and character-defining qualities, as well as responsible concern for appropriate balance in determining level of effort.

It may also be possible to define management zones within a landscape for project purposes and to limit assessment of project effects to resources within these zones. Such management zones should be historically defined areas or physically or functionally separate units, such as a scenic corridor or botanical garden located within a recreation area, or a historic water conveyance system in a rural community. When the responsible federal agency and the SHPO agree that activities within particular zones have little potential for involving other parts of a large landscape, project effects could be assessed on these zones alone, without conducting effect studies on other parts of the landscape. Management zones could be appropriate where an agency has continuing maintenance or project activities on a relatively small or discrete element of a large landscape, such as a narrow transportation corridor that bisects a vast agricultural landscape. See Preservation Brief 36 for further discussion of management zones.