What are these white circles in Nevada?

You can probably find circles like this at other military testing facilities.

These are artillery firing targets meant for "Circular Error Probable" and Time on Target related calibrations and training. During WW1 and WW2, it was found that most artillery kills happen within seconds of the attack starting, because once the artillery has started to impact, the soldiers are quickly rushing for cover. Because of this, artillery soldiers found that the best way to get optimal impact from artillery was to ensure that all shells landed roughly in the same area and at the same time, like a high-powered shotgun blast. These circles are used to determine how closely grouped the shells are, and because the ground is completely flat, it also allows for easy monitoring of the impacts to verify how close they are in time. If you look over the hills to the west, there is a similar circle that has more obvious impact markings. The circles are roughly 100 meters apart so it's easy to gauge how many shells land within 100 meters of the target.

As Michael Seifert has said it's part of the Nevada Test and Training Range, between your noted circles (GM: 37.48781°N 116.22827°W) and the ones approx 2km NNW (GM: 37.51303°N 116.24306°W) and being so close to Area 51 (Groom Lake) I'm going to go with bombing targets as a most likely explanation.

On looking closely though I found more curious things in the immediate area:

• (37.51107°N 116.25754°W) + (37.47446°N 116.25019°W) + (37.47963°N 116.25537°W) + (37.51284°N 116.25085°W) + (37.51704°N 116.2563°W) + (37.50663°N 116.25092°W) + (and many more) seem to my eye to be either shielded observation points or certainly deliberately placed concrete as they are angled, in my opinion, towards the centre of your target.

• A 15m/50ft aligned grid (37.48853°N 116.21334°W)

• 3 rectangular profiled objects for want of a better term (37.51124°N 116.25214°W) (37.51183°N 116.25489°W) (37.51492°N 116.25388°W) possibly bunkers.

• The various earthworks around the lakebed are also interesting, they will be there to pull out groundwater and allow people and equipment to get across without getting bogged down.

I spent far too long looking at the area to admit but it was interesting, thank you for bringing it to my attention.