California buckeye?

I don't think it is a CA buckeye. It does not make buckeyes (I've never seen any in 32 years), and the leaves do not make clusters of 5, but grow along the stems on alternate sides. Also, the flower panicles are not as dense - much more wispy. Here is a blown up photo which might be helpful:

Google Image Search (click on the green text to see the suggested types) suggested Prunus padus ‘Watereri’ Bird cherry Watereri; Prunus lusitanica (Portugal Laurel); Celtis occidentalis or Hackberry also known as nettletree, sugarberry, beaverwood, northern hackberry, and American hackberry; Prunus virginiana - chokecherry and potentially other similar types. All of the images are quite similar from the presented photos. Which looks more like what you have? Does yours fruit?

Chinese privet (ligustrum?)

Portuguese laurel? I am guessing laurel.

Based on the length and droopiness of the flower sprays, it is most likely Prunus lusitanica, the Portuguese laurel, which, along with the closely-related English laurel (Prunus laurocerasus), has become naturalized here in the San Francisco Bay Area and is not uncommonly encountered in the wild, especially in riparian areas. The English laurel's inflorescences tend to be more upright.

You guys are amazing! Thank you all - I always get faster and more accurate answers on the Antique Rose forum about non rose plants than when I try any specific other forum. Prunus lusitanica it is, at least mine looks exactly like the pictures of it. It does fruit - those long panicals of flowers turn into blue black berries, which are very pretty too.

Jackie

I'm glad you determined what it is, @jacqueline9CA. Google Image Search very often provides good information when I've used it, and it's easy (and FREE!). Wikipedia states you probably don't want to do much with the foliage, though. "The leaves of Prunus lusitanica contain cyanide and will release this into the environment if burnt[18] or if crushed.[19] The fruit is somewhat edible if fully ripe, but if it is bitter, it is toxic and should not be eaten."

Pretty much all of genus Prunus contains cyanide, including almonds, apples, peaches, nectarines, etc. The nuts of feral seedling almonds (common around Livermore) are often exceedingly bitter and full of cyanide, enough to kill humans if enough nuts are eaten. The almond flavor is, in part, the taste of cyanide. Apparently it's a single gene mutation that shuts off ability to produce cyanide and that led to the development of non-lethal domesticated almonds: How Almonds Went From Deadly To Delicious. The nuts inside the pits of peaches, nectarines, etc. are also not particularly safe to eat.