I didn't answer Michael Hobbs' thoughtful questions as thoroughly as could
have been done, so here are some more observations:

The owl was indeed still around as recently as Sunday (March 2).

It was definitely silent the one time I was fortunate enough to see it.
Nor have I heard anyone say that it had been calling.

When it is seen it is actively hunting, changing perches fairly often and
flying short distances between them. It has frequently been seen plunging
into the salal or other undergrowth, but has not been observed to take any
prey. It seems quite tame, oblivious to people and horses. But there
haven't been hordes of tripod-bearing enthusiasts out there pursuing it,
either.

Most (practically all?) sightings have been in the middle part of the day,
from 11 to 2 or so. Once found, though, the owl has been tracked (easily,
apparently) later than that. The trick is to find it initially.

There has also been a reliable Snowy Owl in the park. It is usually
sitting on top of one of the big power poles in the power-line cut that
bisects the park north to south.

Hal Opperman