Unnamed spotting

These are really common on the oaks in California. They don't appear to harm the tree... for all we know there is even some benefit to the tree in harboring wasps. Oak galls are poorly understood but there are many, many different kinds.

Thanks for the info. You are correct Here is Wikipedia info on oak apples.

"An oak apple is a mutation of an oak leaf caused by chemicals injected by the larva of certain kinds of gall wasp. They are so called because the gall, which can measure up to 5 cm in diameter but is normally only approximately 2 cm, somewhat resembles an apple. Considerable confusion exists in the general 'literature' between the oak apple and oak marble galls. The oak marble is frequently called the oak apple due to the superficial resemblance and the preponderance of the oak marble gall in the wild.

European oak apples are caused by the Biorhiza pallida gall wasp and American oak apples by Amphibolips confluenta.[1]

Oak apples may be brownish or reddish.

The wasp larvae that live inside oak apples are a good source of bait for fishing, and also are useful as a survival food.[citation needed]"

Yep, looks just like an oak apple!

they are oak apples

The balls were not spikey. Looking at them I got the impression they did not belong on the tree. I would agree with your first assumption that they are a parasite.

Were the balls spikey, with green and red colors? This could be a Strawberry Tree, also known as the Apple of Cain, Arbutus Unedo. It is not native, but not uncommon in the Portland area.

Interesting. By the leaves, it appears to be an oak tree. Those yellow balls on the leaves may be some sort of parasite.