For an observation of the host see https://www.inaturalist.ca/observations/215640541
For an observation after parasitizing fungi, see https://www.inaturalist.ca/observations/215640550 .
Not sure on id looks like Spilomyia longicornis but no obs on West Coast. If you look carefully you can see a yellow v on the back.
I think these are slug eggs
Under a decaying log
I didn't see any slugs nearby