I stopped by Peace Valley this afternoon to take another look at the loons. As reported earlier on PABirds, in the same general area where I reported a Pacific Loon there was an obvious adult Red-throated Loon. After taking a good look at this bird, I really don't think its the same bird I saw this morning. The bird I saw this morning looked darker on the neck including at least a partial necklace below the throat, and this morning I didn't see white above the eye on the face or white on the sides of the body. I didn't think the bird this morning held its bill at as elevated an angle as the bird this morning, and (this is pretty subjective and subject to change based on a bird's mood) seemed to have a differently proportioned and rounder head with a steeper angle between the bill and forehead.
However, as a member of the "reality-based community", I'm really uncomfortable with the "two bird theory" that the Pacific Loon flew off after I left to be replaced within the hour by a Red-throated Loon. Is it possible that earlier this morning in the snow and poor light that I didn't get as good of a look as I thought? While I don't think so, I would be an idiot not to at least consider it a possibility. Viewing conditions were admittedly not 100% ideal, so I have to at least accept the possibility that my eyes, brain, and/or optics could have failed me.
Since I have to acknowledge even the slightest possibility of observer error, I can't be 100% certain about my sighting this morning, and humbly accept that the ID failure theory probably seems more plausible to most folks. Without a photo or multiple observer confirmation, I'm left without satisfaction and only an increased desire to get my hands on a workable digiscope setup--and the hope to redeem myself with a truly verifiable rarity sighting next time!