(a) Determination of need for modifications. After designation, the modification of the boundaries of a natural landmark, and/or revision of information about it, may be appropriate. For example, because of new information or changes in the condition of an NNL, the boundary may have to be reduced or expanded or information about the NNL may have to be revised. Additional study may reveal that the area has nationally significant values that had not been previously documented. The NPS determines that landmark modifications are necessary through administration of the program. In addition, the NPS may receive suggestions for landmark modifications from other Federal agencies, State natural area programs, and other public and private organizations or individuals. The NPS determines the validity of these suggestions by applying the natural landmark criteria or by conducting additional study.

(b) Boundary expansion. (1) Three justifications exist for enlarging the boundary of a national natural landmark: better documentation of the extent of nationally significant features, professional error in the original designation, or additional landowners with nationally significant features on their property desiring the designation.

(2) If the NPS determines that an expansion of the boundary of the national natural landmark is appropriate, it will use the designation process outlined in § 62.4(b) through (j). If a boundary is expanded, only the owners in the newly considered but as yet not designated portion of the area are notified and asked if they object to designation.

(c) Boundary reduction. Two justifications exist for reducing the boundary of a national natural landmark: Loss of integrity of the natural features or professional error in the original designation. If the NPS determines that a reduction in the national natural landmark boundary is indicated, the designation removal process outlined in § 62.8 is used.

(d) Change in description of values. If the NPS determines that a change in the description of the national natural landmark's nationally significant values is warranted, the NPS prepares the recommended changes and the Director submits the changes and all supportive documentation to the National Park System Advisory Board. The Advisory Board reviews the information submitted by the Director and makes recommendations to the Secretary. The Secretary reviews the supportive documentation and the recommendations of the board, and may approve changes in the description of a landmark's nationally significant values.

(e) Minor technical corrections. Minor technical corrections to a national natural landmark boundary and other administrative changes in landmark documentation not covered under paragraphs (a) through (d) of this section may be approved by the Director without a review by the Advisory Board or the approval by the Secretary. Minor technical boundary corrections are defined as those that involve a change in less than five percent of the total area of the national natural landmark. The NPS notifies owners of proposed minor technical boundary corrections or other administrative changes in documentation, as described in this paragraph (e). Based upon owner response to this notification, the NPS determines whether the proposed change is a minor technical correction to landmark documentation that can be made administratively or whether the procedures outlined in § 62.4(d) through (j) must be followed.