A living geyser is sterile ground. The water is near boiling, it is loaded with dissolved silica, and as it cools on the surface that silica precipitates out as geyserite, a hard pale crust that builds up grain by grain over centuries. Nothing puts down roots in it, because anything that tried would be cooked.

So a tree growing out of a geyserite mound is a clock. It says the plumbing underneath has shut off, and has been shut off long enough for the surface to cool, for the crust to weather, and for enough soil to gather in the cracks to support a juniper. Geothermal systems shift constantly: channels seal with their own mineral deposits, earthquakes reroute them, and a feature that was a geyser within living memory can be dead ground now.

Junipers are the right tree for the job. They will hold on in almost nothing, they grow slowly enough that a small one can be old, and they are the species you find again and again in this collection taking root where nothing sensible would.