Is there any telltale sign it is not a Golden Eagle? The person seems certain it is, because it was apparently quite large. I’ve lived in California my entire life and have had zero eagle sightings, but they do live here. Any tips on when and where to find them? They are just magnificent in size, at least the Golden breed. I’ve seen a couple of bald eagles in Washington state, but never here.
The easiest sign for a beginner is the pale belly. Golden eagles are dark-brown underneath all the way (not just the head). The Red Tailed Hawk is one of the largest Buteos in the US, and a large female can sometimes be confused for an eagle from a large distance (until a true eagle comes along), so it's better to look at plumage than at size. There
is a dark morph of the Red-Tailed Hawk that is particularly tricky, but luckily the bird in this picture is not a dark morph at all.
For a slightly more experience birder, the main sign is a completely different body build of a hawk (Buteo) versus that of a true eagle (Aquila). Buteos are stocky, have short legs that are easily hidden in belly feathers, relatively short necks, and their overall profile looks "plump." An eagle has
much longer, almost fully feathered legs, longer neck, and a significantly longer tail. In fact, many people who observe an eagle for the first time think, "my my what long legs he has" (to which the eagle might say, "all the better to stab you with if you were a marmot or a fox"). One exception -- fish eagles, including Bald Eagle, have somewhat shorter legs than Aquila eagles do, but are unmistakable for other reasons, such as the massive bill.
I only got to spend time watching Goldens in Europe, where they were hunting Brown Hares on grassy subalpine slopes. One day I will find them here in the US, one day...