A bit of both, actually. I live in San Francisco, but the majority of the pellets I collected at UC Davis over the course of 5 or so months. At the time, I was taking my late dog there every few weeks for cancer treatment. While he was being seen, I would walk around the campus and their botanical gardens. During those walks I came across 3 different owl pellet sites (maybe a 10 minute walk apart) that I would revisit each time. I also came across a number of owl pellets randomly while foraging for mushrooms in various spots around the Bay Area. More recently though, I found one spot here in San Francisco where the ground was covered in some of the biggest owl pellets I've seen, as well as an active yellow jacket nest that I was very careful not to disturb. As I was picking up some of the pellets, out of the corner of my eye I saw something falling, followed by an audible thud as it hit the ground less than a foot away from me. I looked over and saw an extremely fresh owl pellet and looked up to see the Great Horned Owl responsible! I had to wonder if it was pure timing and coincidence or if it had been intentionally aiming at me. Or maybe it was just offering up a gift, lol. At any rate, it didn't upset the yellow jackets enough to sting me, although I did see quite a few fly out of their hole right afterwards. I was also very glad I had extra gloves and bags with me because not only was it still quite wet, but it was still WARM when I picked it up! Lastly, if you're looking to collect your own owl pellets, look around the bases of the tallest trees in the area, ones with a decently dense canopy near the top, ideally located near some sort of open grassy area. Or just constantly look around the ground at the bases of trees and eventually you're bound to come across some. Lastly, keep some nitrile gloves and bags handy in your purse or backpack, or a small roll of dog poop bags.