I don't think they're a source of materials used in the project (my first guess) because they can be found quite far away from the site, are present across varied terrain, and lack road access and indicators of work (eg tailings). Such uniformity in natural features always piques my interest. Will just be one of those endless mysteries of the desert, I suppose.
Those look a lot like creosote rings [1]. Creosote's native to southern Nevada and grows in clonal colonies that end up looking like rings, and that looks like a nice wide place where water would gather.