C.R.S. § 31-4-103

(1) Within thirty days of the mayor’s death, disability, resignation, or other vacation of the mayor’s office, the city council shall appoint a person possessed of all statutory qualifications or order a special election as soon as practicable to fill the vacancy until the term of office of a successor elected at the next regular election has commenced, as provided in section 31-4-105 , and the city council may appoint a registered elector to act as mayor until the special election. The special election shall be conducted in accordance with the provisions of the “Colorado Municipal Election Code of 1965”. If the council lacks a sufficient number of members in office to establish a quorum to choose a successor or order an election, the vacancy shall be filled in the manner provided by section 31-4-108 (3). (2) The city council may appoint one of their own number acting mayor or mayor pro tem who is entitled to act as mayor in case the mayor is absent from the city or is for any reason temporarily unable to perform the duties of his office.