Prunus avium is common.

Thanks for the quick reply. Still wondering if it's considered a weed tree (since I see them everywhere) or desirable (since I see them everywhere) or... ? any thoughts, opinions? still curious :)

Could be any flowering cherry. Always a joy this time of year, and maybe a pain later (depending on the tree, of course). My feeling is that we should enjoy all the lovely ones around, but we don't need to own one, too.

"Tall as cottonwoods" wouldn't be most Japanese (flowering) cherries, whereas naturalized sweet cherry is abundant and tall here. It reseeds and also suckers to form groves, can be easily seen well scattered through some neighborhoods at flowering time--both planted (as 'Bing', 'Lambert', 'Rainier'...or as a rootstock for 'Kanzan' and friends) and as a weed. Those growing among native trees on undeveloped hillsides will often be as tall or taller than native trees around them. And sweet cherry sometimes crosses with native but rather dissimilar bitter cherry (Prunus emarginata) to produce Puget cherry, an apparently sterile hybrid. Many (most?) of these hybrid seedlings are noticeable for having a more luminous appearing, somewhat greenish white flower color than the parents; otherwise they tend to look like sweet cherries with somewhat smaller parts.