It was once easy to go to a back mountain general store and get blasting caps. I’m not saying they’d sell to a kid they didn’t know, but they were there. My father said it wasn’t hard to find such things in Pennsylvania growing up, but PA is mining country. According to him explosives were used for removing recalcitrant stumps, and were the kind of thing that were picked up intown, sans training, ID, or common sense.
My spouse’s brother once, as a teen, went spelunking in an abandoned mine and found a few sticks of old dynamite. It was all fun and games until somebody explaind about how dangerous it was and that touching that stuff could lead to headaches that would be suicide worthy. That ended well, but it could easily have ended up badly. I am also confident that the unlikely success added to the local lore about driving to the 49 and looking for abandoned mines.
For me, fear of weirdos in caves was instilled by the movie Mazes and Monsters.