The PNW native dogwoods, cornus nuttallii - Pacific Dogwood, frequently (but not every year) will rebloom in late summer, early fall.

Thank you both. My friend is from Portland and he thought it was very late for a dogwood to be flowering (so did I),

It is very late for a dogwood to be flowering :-) But as noted, Pacific dogwoods in the wild often throw a few flowers in late summer/early fall. It could also be something other than the native species......like a hybrid with native parentage (Eddie's White Wonder). Native dogwoods seldom respond well to actual cultivation in a garden. Much like our native Pacific madrone, these trees spring up best in the wild and are not often found for sale outside of a native plant nursery.

It doesn't look like the Eddie hybrid and I don't think that re-blooms in summer either. Whereas the pure native - which this looks like - often does.

And often opens a lot of heads during the second show.

This was in someone's front yard on Mt Tabor in Portland. "Dogwood" is probably good enough for us. We thought the flowers looked very much like dogwood, but we were surprised to see it blooming so late, and we didn't think the leaves looked especially dogwoody. (I think of dogwood leaves as having curving veins, and this looked more like a generic leaf)

Unless one of the Orton hybrids, which may be too new on the local market for one 20 ft. tall to be likely it's Pacific dogwood, an otherwise more or less unique tree.