You might call it shadbush like my parents did, or saskatoon, as they do in Canada, or juneberry--the name you might see in the supermarket--or more regionally shadblow, sarvis or sarvisberry, sugarplum, wild-plum or chuckley pear.
All of these are names for native Amelanchier species, mainly A. alnifolia, though there are approximately 10 species native to North America (link: USDA plants)