Robert Winbourn would die in office on August 7, 1930. John Underwood was appointed to fill the vacancy and served until his own death in a car crash on January 11, 1931. The seat remained vacant for the remaining day of the term.
Source for Popular Vote data: Colorado Secretary of State. Abstract of Votes Cast at a General Election Held on Tuesday, November 6, A.D. 1928, Colorado Secretary of State (https://www.sos.state.co.us/pubs/elections/Results/Abstract/pdf/1900-1999/1928AbstractBook.pdf) (accessed 13 Dec 2023)