My suspicion is that the prominently paved structure you're referring to is related to the publicly known Junction Ranch radar range located a half-dozen miles

My suspicion is that the prominently paved structure you're referring to is related to the publicly known Junction Ranch radar range located a half-dozen miles to the south, and indeed the eastern of the two long paved roads (which you can tell are elevated somewhat from the ground, as they have culverts under) appears to have antennas at the north end. There also appear to be some kind of portable towers set up around the area. However, the farther west of the two seems to have a small structure made up of shipping containers or similar portables. This looks more like a setup for explosives testing, which you can see more of to the NNW. I'm not sure what to make of it besides to speculate that it could be for RF shielding. Like most military ranges of its size, though, China Lake's back lot is full of so much miscellany that it's hard to know what's even from this decade, much less what anything is for. The structure you point out is fairly new, built since 2007, so it's a good bet it's still for something current. That said I find it very unlikely they would have provided particularly accurate coordinates for the NOTAM. They probably used the geographical center of the range's northern part or something similarly unhelpful but justifiable.