Mark Allen Bonner was 23 when he was last seen in Boulder, Colorado, on March 20, 1978. He had been house-sitting at a residence on Neva Road north of Boulder. No witnesses have been identified for his last movements, and both his personal belongings and his vehicle were never recovered.

Authorities investigated possible links to drug trafficking early on, but that theory was never proven. The Boulder County Sheriff’s Office continues to list Bonner as missing and the investigation is described as cold but not closed. He is described as 6 feet 3 inches, with blond hair and blue eyes.

If anyone knew Mark, his routines, associates, or saw his vehicle around Neva Road on or after March 20, 1978, please contact the Boulder County Sheriff’s Office with any information.