With flowers that pink it could be 'Thundercloud' or it could be 'Krauter's Vesuvius'. That's if it was a clone from a nursery. If it was instead grown from seed, not named and put into commercial production then it won't have its own cultivar name.

People do sometimes grow their own saucer magnolias, plum trees and other kinds with large, noticeable and easily handled fruits and plant them out. I was headed out toward Everson or otherwise in the vicinity once, stopped at a roadside stand or other attraction and asked about a grouping of purple plums that was blooming right there. The reply was that the neighbor had grown them all from pits.

Thanks so much, bboy! I'm leaning towards 'Thundercloud' give the photos I've seen on-line. But it's a close call. And, as you point out, nothing can be definitive since I haven't a clue when and how the tree was planted.

There's a dichotomous key in the 1992 Timber Press book Purple-leaf Plums by Seattle resident Arthur Lee Jacobson. If you find a copy at a library or bookstore (the Lynnwood Barnes & Noble was still putting out copies a few years ago) you will see that on page 69 he says that the P. cerasifera forms that are "obviously pink" at flowering time "cannot be distinguished by examining only flowering twigs alone". And that 'Krauter's Vesuvius' is "common in the western United States", 'Nigra' is "common" and 'Thundercloud' is "common in North America". Since 'Nigra' is basically only offered in BC in this region that leaves the other two as the main candidates.