I loved it, Graeme!!
As someone who lives in a wildfire prone area, this really hit home to me. Wildfires are a real and present danger, and sadly not uncommon, either in the area Graeme wrote about, or here, or in many other places.
I made a few notes as I read;
I loved the shirtless arrival carrying the billy can! :-)
A cliff?? Hrmmm, yes, a cliff in your story...
I found the bone-setting well done and believable. I also liked Brian's inventiveness.
I love Brian's inner battle with his conscience and fears.
Brian's bedside manner could use a bit of work. :-) "You're badly hurt, so just relax". I think it's very appropriate, but it also made me smile.
"No, and we couldn't, anyway. It's a Total Fire Ban day." That made me chuckle. Believable because people say odd things under stress, and IMHO it served to highlight their stress.
"We go that way and we die. We've got to get to the waterfall." Brilliant! This part struck me as the most clever of all. When the story started, i was wondering how the heck they would get out of the canyon; those become firestorms all too often. Behind the waterfall would be about their only hope. It would still be risky, due to the smoke, but it would be the best chance they had.
Loved the bittersweet ending. You didn't go for the clich