Final answer:
Aven's dad, David, found a dulcimer at Stagecoach Pass.
Step-by-step explanation:
The musical instrument that Aven's dad, David, found at Stagecoach Pass was a dulcimer. However, it was not widely used by dance-oriented bluegrass groups because it couldn't be heard at a barn dance. Banjos, fiddles, and guitars were more popular choices due to their louder sound. The mandolin, another instrument used in bluegrass, was played rhythmically and percussively to increase its volume.