So this is one that has been bugging me forever. It was a book about a small town (in America, I am fairly sure) where a metallic pyramid (iirc made of black metal) shows up, the town is trapped in a force field, and (I think) some sort of alien monster hunts the locals. I remember that at least part of the book was set in a high school (the pyramid may have been located there) and the protagonists may have been high school kids. Setting may have been the US west (desert).

I got the book from my local library, and I want to say it had a cover with a lot of yellow, but of course covers vary so wildly, I doubt this is super helpful.

I read this book as a teenager, call it 35 years ago (circa 1988), and it was almost certainly older than that (my local library had a lot of 50s/60s SF).

It is not "under the dome", by King.

I've googled, checked TV Tropes, and generally dug around on and off for a few years. No dice so far.