Yellowstone is earth’s largest active geyser field and I was most mindful of this when trying to find a location that encapsulated the park’s identity and character. I recognised that I also needed depth – the riddle here was that this required good light and if the trees were also to be full of snow, I was asking for a demanding climatic combination. Without fresh snow, there was no picture here. Luckily on my last day in Yellowstone, “The weather gods” were favourable and then all that was left was the need for some bison to give context and interest.