Derek, a serious answer to your question is that the early ones didn't have TV and Professional Football to waste time on. They knew their enviroment intimatly. All their recesources came from the natural world and they were always on the lookout for new and different rocks, plants, animals.
As soon as you find something, you figure out what you can use it for.
The early ones were not dumb. In fact they were just as smart as today. They had their geniuses too. Have you ever held a Clovis point in you hand. Amazing the dexterity and intimate knowledge of the stone needed to make one of those. I can't do it, and I've got books and computers to show me how.

And Trade - It was far more widespread than we thought 10 years ago. In N. America flint from the hills of Texas was traded all the way to Canada.
In the British Isles chalk from the south and coal from the midlands are found at almost every site. These only hint at the vast and active trade of the times.

Of course they knew Bluestone existed, and where it was found. Now all you need is a will to make Stonehenge and Woodhenge. Humans will find a way. We always have.