The following information courtesy of his great-great nephew John Gleason:
Claggett Spangler of Hagerstown, Maryland was active mostly in Maryland, Harpers Ferry, Virginia, as well as Pennsylvania. He did a lot of landscapes and a few portraits (R.E. Lee), some family members and of himself. His work also included European streets and countryside scenes, some true to life and some in an impressionist style.
He passed away in 1911, not 1941.
Source: Washington County Museum in Hagerstown, Maryland.