C.R.S. § 42-4-1106

(1) Where the average grade is six percent or more uphill for at least one mile, no person shall operate a motor vehicle in the far left lane of traffic of interstate 70 at a speed of less than the lower of ten miles per hour below the speed limit or the minimum speed set by the department of transportation, except if: (a) Necessary to obey traffic control devices; (b) Necessary to exit or enter interstate 70; (c) Weather or traffic conditions require speeds slower than the speed limit necessary under section 42-4-1101 ; or (d) Necessary because of a lane closure or blockage. (2) The department of transportation shall post signs giving the public notice of this section.