Colo. Rev. Stat. § 31-25-1119
No action shall be commenced to foreclose the lien created by any bonds or warrants issued pursuant to the making of any public improvement, including the establishment, widening, grading, paving, or other improvement of any alley, street, or road, special districts for internal improvement, local improvements by cities or towns, streets, sewers, district sanitary sewers, storm sewers, or subdistricts thereof, municipal special assessment, conservancy districts, or any other such improvement for which taxing authority is authorized by law to make assessments and collect taxes for the purpose of retiring said bonds or warrants, unless the action is commenced within fifteen years from the date of maturity of the last issue of said bonds.
C.R.S. § 31-25-1119