Where's the Nitre?

Hey guys,

First of all, LOVE THE GAME. I’m a huge fan of survivalism and primitive living skills, and this is the first game I’ve ever seen that fits those descriptors so well! Here’s my question:

I found a flint lock pistol today and I am looking for Nitre, so that I can craft some black powder. I’ve traveled with the bull boat a few times and haven’t had any luck yet. How do I find it and what does it look like? The documentation page just shows a pile of ash…

I’ve actually been able to find nitre in past plays, refine it to saltpeter, and craft the black powder. I’ve also found the flint lock pistol on one other occasion. I have never been able to do these 2 things in the same game though! Really anxious to fire this pistol!!