He paired with Michael Martin Murphey in the 1960s pop group The Lewis & Clarke Expedition, which recorded a pop album in 1967 for Colgems, the label that released The Monkees. The band was said to have gotten the deal with Colgems through Murphey's, Castleman's, and bassist John London's associations with Michael Nesmith – a native of Dallas.
Castleman was the inventor of the palm pedal, a device that allows guitar players to execute pedal steel-style string bends. He made his original prototype in 1968. It is marketed under the name Bigsby Palm Pedal. The original patent has expired, allowing other vendors to market similar devices, but the Bigsby/Castleman version is the original.
- Boomer Castleman at Allmusic.com