Yellowstone

Despite its green (for now – see next) appearance, this region is the product of a terrible cataclysm. 650,000 years ago a huge pool of magma just below the surface broke through and split the crust in a circle of eruptions. The centre collapsed forming a caldera 50 miles wide. Eruptions continued until very recently, pushing great lava flows out across the floor of the crater, which are still very much in evidence. The magma is again building up underneath and pockets of heat produce geothermal vents all over the area. The last eruption was one of a series at this hotspot that have been recently, and perhaps worryingly, at roughly 600,000 year intervals.
There are more geysers, hot springs and thermal vents in Yellowstone than the rest of the world put together. The flora and fauna provide a calming patina that does not entirely disguise the raw energy ready to burst out from beneath. There are many areas where you can see the steam rising almost from horizon to horizon. There are deep clear, extraordinarily blue pools of boiling water, steaming away; and of course the geysers are spectacular. We visited Old Faithful, the most famous, though not as regular as it used to be. However, when we got there, a rumour went round that it would blow at 1.30, and sure enough it did. Steam emerged, then a few spurts of scalding water, then sudden;ly a huge plume 15 or 20m high for a few seconds, gradually subsiding to just steam again. However, the razzmatazz in this area we found less attractive than some of the other less visited thermal sites.
Add to all the volcanic stuff the action of glaciers and fast moving rivers, which have rapidly cut deep, narrow gorges into the whole area, and you can imagine what a fascinating area this is to visit.
Finally, the endless treescapes and glimpses of wildlife add yet another level of interest. We saw many buffalo, deer and elk, and very fleetingly, a cayote and even, yes, a black bear, that ran across the road two cars ahead of us.
We were lucky to go in autumn when visitor numbers are much lower, but we had perfect weather. Bright sunshine all the time, temperatures dipping at night but perfect for walking around in the day. We have been over a mile above sea level (or more – over 3000m on some passes) and you can really feel the shortage of oxygen, that makes you at times catch your breath.