I don't want to make you lose any more sleep but......I have come across a fire smoldering under 8' of snow at the end of March.
Imagine this, you’re busting through 2' of powder on a great base and you stop to water up, when you smell heat (something you acquire from being a fire fighter), We sniff it out and come across smoke rising out of the snow????
Yeah, I thought I had seen and heard a lot of stories fighting fires but nothing like this. We were on the edge of a wilderness area in Utah (Utah is usually rather dry most of the year except for winter). Long story longer the fire was burning because of a left over fire that some hikers or sledders had started some time earlier in the season. We never found the fire pit, I guess it had been covered over by new snow but that doesn’t mean the hot coals were out! In spring the snow pack separates somewhat from the ground, making a few inches gap along large areas of ground. Even though the snow is 10’ deep there will be this little pocket of air between the snow pack and ground, it is still too cold in March for the snow to melt so the conditions on the ground are similar to mid October, dry and ready to burn (Utah winters begin when summer ends, not really a fall rainy season like most Mountain regions, so the ground is bone dry when the snow flies). The fire had melted through the snow pack, fell into this 3-6 inch deep gap under the snow and smoldered until the duff (dry piles of pine needles/leafs/pinecones) ignited. The fire had spread some distance when we found it still smoldering, hot and smok’n. Like I said we couldn’t ever fine the exact location of the fire pit but it looked like it had traveled some distance up the slightly sloped terrain until we found it near a ridge.
So to calm your fears, I’m no expert but I think the fire you guys had camping will be fine, a lake on one side, rock slabs around the others, rain for the next two months, you should feel confident you don’t need to hike back up their to just make sure the fire doesn’t need another dousing
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BTW nice picts, I love to see young ones getting out and partaking of the wild outdoors!