HPL in Astounding Stories

Because of its length, At the Mountains of Madness appeared in three consecutive issues of Astounding Stories (February–April 1936). Each installment featured illustrations (by Howard Brown), noteworthy as some of the earliest artwork connected to a Lovecraft tale. A few are especially significant, as they provide the first published depictions of the Old Ones (Elder Things) and shoggoths.

The first issue from the February 1936 issue shows the base camp of the Lake Expedition, with the city of the Old Ones in the distance.

This issue also includes two illustrations of the Old Ones themselves.  The March 1936 issue opens with a depiction of not just the Old Ones and their city but also a shoggoth, which looks very similar to the one that appears on the cover of the February issue. We then get more of both the Old Ones and their city.  The March 1936 issue contains only a single illustration, again of the city of the Old Ones. At the bottom right, you can see two of the expedition members fleeing the city ahead of the shoggoth (not depicted, so far as I can tell).
In my opinion, these are all really striking illustrations – and apparently Lovecraft agreed. In a letter to August Derleth, he stated that, "The illustrator drew the nameless Entities precisely as I imagined them." Very high praise indeed! 
I'll have more to say about the illustrations from "The Shadow Out of Time," I'll save that for yet another post.