Mosko taught at the California Institute for the Arts, known as CalArts, for most of the last 30 years. He helped to found the California EAR Unit, and led the San Francisco Contemporary Music Players, Boston's Griffin Ensemble, and the Chicago Contemporary Players.

In addition, he was music director for the Los Angeles Olympic Arts Festival's Contemporary Music Festival in 1984, and directed a Philip Glass festival in Los Angeles in 1987. He guest-conducted many ensembles, including the Los Angeles Philharmonic and San Francisco Symphony.

His compositions, critic Mark Swed told the Times, "were written in an abstract style that has gone out of fashion." They were performed by the San Francisco Symphony, the Los Angeles Philharmonic, and the Aspen Festival Orchestra, among other groups, and have been heard at the Ojai and Tanglewood festivals.