(a) Introduction.

1. (1) National significance describes an area that is one of the best examples of a biological or geological feature known to be characteristic of a given natural region. Such features include terrestrial and aquatic ecosystems; geologic structures, exposures and landforms that record active geologic processes or portions of earth history; and fossil evidence of biological evolution. Because the general character of natural diversity is regionally distinct and correlated with broad patterns of physiography, many types of natural features are entirely inside one of the 33 physiographic provinces of the nation, as defined by Fenneman (Physiographic Divisions of the United States, 1928) and modified as needed by the NPS.
2. (2) Because no uniform, nationally applicable classification scheme for biological communities or geological features is accepted and used by the majority of organizations involved in natural-area inventories, a classification system for each inventory of a natural region was developed to identify the types of regionally characteristic natural features sought for representation on the National Registry of Natural Landmarks. Most types represent the scale of distinct biological communities or individual geological, paleontological, or physiographic features, most of which can be mapped at the Earth's surface at 1:24,000 scale or are traceable in the subsurface. In some cases, the NPS may further evaluate only a significant segment of a given natural feature, where the segment is biologically or geologically representative and where the entire feature is so large as to be impracticable for natural landmark consideration (e.g., a mountain range). Almost two-thirds of all national natural landmarks range from about 10 to 5,000 acres, but some are larger or smaller because of the wide variety of natural features recognized by the National Natural Landmarks Program.

(b) Criteria. NPS uses the following criteria to evaluate the relative quality of areas as examples of regionally characteristic natural features:

1. (1) Primary criteria. Primary criteria for a specific type of natural feature are the main basis for selection and are described in the following table:

   Criterion	Description	Example
   Illustrative character	Area exhibits a combination of well-developed components that are recognized in the appropriate scientific literature as characteristic of a particular type of natural feature. Should be unusually illustrative, rather than merely statistically representative	Alpine glacier with classic shape, unusual number of glaciological structures like crevasses, and well-developed bordering moraine sequences.
   Present condition	Area has been less disturbed by humans than other areas	Large beech maple forest, only a small portion of which has been logged.

2. (2) Secondary criteria. Secondary criteria are provided for additional consideration, if two or more similar area cannot be ranked using the primary criteria. Secondary criteria are described in the following table:

   Criterion	Description	Example
   Diversity	In addition to its primary natural feature, area contains high quality examples of other biological and/or geological features or processes	Composite volcano that also illustrates geothermal phenomena.
   Rarity	In addition to its primary natural feature, area contains rare geological or paleontological feature or biological community or provides high quality habitat for one or more rare, threatened, or endangered species	Badlands, including strata that contain rare fossils.
   Value for Science and Education	Area contains known or potential information as a result of its association with significant scientific discovery, concept, or exceptionally extensive and long term record of on-site research and therefore offers unusual opportunities for public interpretation of the natural history of the United States	Dunes landscape where process of ecological succession was noted for first time.