unidentified spotting

Description:

Scores of white insect remnants about 1" long. To be clear: this spotting was not alive.

Habitat:

Pacific Northwest montane forest.

Notes:

Spotted attached to a vertical side of a rock along the shore of East Lake in Newberry Crater National Volcanic Monument in central Oregon. I take these insect remnants to be molted damselfly or dragonfly exoskeletons. The first image is a "mid-distance" view; the second is of a single specimen; the third is an "overview", but even it does not capture the full extent of these remnants. Comment: I've seen a few molted cicada exoskeletons; I've never previously seen anything like this.