What is this fragrant bush growing in the gold country in California foothills about 2000ft altitude?
Deutzia scabra, (cultivar might be 'Plena')is a deciduous shrub with somewhat cascading limbs covered in fragrant white (sometimes pink) star shaped flowers. Tolerates almost any soil, but does best when it is moist & rich. It is native to Japan and China, but has been a classic in western gardens for many years.
It is weird if you found this in the middle of a wild area, but in my opinion it looks more like Deutzia than Philadelphus. Western Philadelphus does not have a star shaped flower like Deutzia. It may be an introduced, escapee plant. It has been introduced to most of the East Coast of the US, parts of the mid-west, & Utah, so it may also be introduced but not documented in California.