C.R.S. § 25-7-304

The attainment program shall provide that emission reduction offsets which exceed those otherwise necessary to the granting of a permit under this part 3 may be preserved for sale or use in the future. Any emission reduction offset so preserved for future use and credit shall be specifically identified either in the state implementation plan or in the permit for the source as to which such offset was originally obtained. Any offsets so preserved and identified shall not in any way be condemned or taken under the provisions of articles 1 to 7 of title 38, C.R.S.