The long descent to West Thumb was engineered for a reveal, with the first view of Yellowstone Lake held back until just before the junction. Trees may have changed the view since. West Thumb itself is a small caldera inside the larger one.
Somebody planned what's about to happen on your left. The nineteen thirties design brought this descent through a triple compound curve to the right, so that Yellowstone Lake would appear just before West Thumb, with its islands and the Absaroka Range in the view. Trees have grown since. It comes late in the descent, so keep watching through them on your left. When it opens, you're looking at the largest high-elevation lake in North America. It sits at seven thousand seven hundred thirty-three feet, about twenty miles long and fourteen wide. The bay you reach first is a volcano's work in its own right. West Thumb is a caldera nested inside the Yellowstone Caldera, about three point seven by five miles, similar in size to Crater Lake. It's somewhere from a hundred sixty to a hundred seventy-four thousand years old. That bay is a hole inside a hole. The junction comes right after that view, and it's the turn people get wrong, so stay with me. West Thumb Geyser Basin is the first right after it.
Photo: NPS Photo / Jacob W. Frank · Public domain (NPS; PD-USGov-NPS)