Sonic Booms Incoming This Week

[DVexile]

First I’ve ever seen an announcement like this. 

They post similar announcements from time to time, but it isn't very frequent.

I’m unclear on where the testing might take place or what altitude.

Sonic booms could be high altitude or deep in the base right?

The least likely thing to be generating a sonic boom there is a low flying aircraft. They could do that kind of testing on the sea range and San Nicolas is a well instrumented impact zone - all off shore where sonic booms aren't a big issue. Probably the same can be said for a high altitude aircraft as well. So I think you are right that it probably isn't likely to be some aircraft zooming around to be photographed.

Whatever it is likely has to have some specific reason to be done on the China Lake land ranges because they avoid generating impactful booms whenever they can. That still leaves a long list of things it could be! There is a rocket sled track there, goes up to Mach 4. They've been building facilities related to hypersonic weapons, but from the little I've seen the big outdoor parts have been more associated with the sub-sonic launch phase of them. Various missiles which go supersonic are often launched from the ground during testing even if they are eventually meant to launch from air platforms. Or maybe it is actually something coming from a supersonic air platform and there just happens to be some sort of special instrumentation on the China Lake ranges not available elsewhere.

Anyway, I've heard a lot of booms from China Lake and I've never been able to see any visual signature associated with such booms.