The Deep was a short-lived band made up of musicians from , who in 1966 traveled to to record a one-time LP, . The band was experimentally progressive, as they were one of the earliest groups to record , before it was adapted by a wider array of musical acts. Although their only failed to achieve success, it later gained acclaim for being considered the earliest work to reference "psychedelic" in its title.
Information on the band is sparse as only one band member had a confirmed musical career prior to recording. The member, Rusty Evans (born Marcus Uzilevsky, 1937, New York City, died December 5, 2015, ), was the Deep's , primary , and a . Evans initially recorded in 1958 as a singer, before performing as a folk musician in the late 1950s and early 1960s. He recorded three albums as Rusty Evans – Songs of Our Land, Railroad Songs (both 1964) and Live at Gerde's Folk City (1965) – and was later a member of the folk group . Musician is also known to have played on The Deep's one and only album, although it is unknown on which tracks he played.
In the early summer of 1966, Evans convinced producer Mark Barkan to help him record a psychedelic album. They secured arrangements with the Philadelphia-based label, the home for fellow protopunk act , for a meager budget of $1200. In August, Evans and Barkan assembled a group of New York musicians to record as the Deep, and they drove in a rundown car to Philadelphia to record what would become the Psychedelic Moods album, which was done in the short period of four days and would necessitate late-night sessions in order to be finished on time. The all-night sessions in August produced not only mind-expanding stream of consciousness ramblings such as "Color Dreams," and "Pink Ether," but also provided the musicians, who were unable to afford a hotel, with a place to sleep, and for one band member in particular, the opportunity to engage in intimate activities with his girlfriend behind an acoustic partition while the tapes were rolling during "When Rain is Black."
While the exact release date of the album has yet to be definitively established, the record is generally considered to have been distributed in October 1966, based on the album's catalogue number. This would credit it as the first official album to include the word "psychedelic" in its title, pre-dating the ' debut, , and the ' eponymous album. The Deep's Psychedelic Moods did not sell well, and the group did not tour to support it. They existed as a studio-only band, and, aside from sessions for their album, produced no other recordings under that name.