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Yellowstone is a big park (2.2 million acres/3,000 sq miles) and a visit takes some planning. Our first day was an orientation in West Yellowstone, a visit to the Junior Ranger station at Madison to get the Junior Ranger packs, a Ranger led walk at Black Sand Basin and a visit to Old Faithful. This kept us in the south west area of the park and kept the driving down to around 50 miles.

After our Orientation Talk – involving animal puppets and other exciting props – we had a good idea of where to visit and what to look for. In a nutshell, geology and wildlife*.

Just after we entered the Park, we saw our first critter jam. A critter jam is a collection of cars pulled up at the side of the road indicating the presence of a critter. This one signalled an Elk strolling through the Madison river. We were so excited! A real Elk! By the time we’d reached the Madison Ranger Station, we’d seen a bald eagle, a herd of elk and a herd of bison. We wouldn’t have stopped for just one Elk anymore!

The Junior Ranger activity was a talk about herbivores and carnivores and the food chain in the Park to a backdrop of the herds of elk and bison Alex, the walking animal encyclopaedia, found the questions a tinsy bit easy which took the Ranger back a bit. We got our Junior Ranger packs, investigated the Ranger tables and moved onto the Black Sand Basin walk via Firehole Falls and lunch.

Our poor Black Sand Basin Ranger was a Yellowstone novice and carried a guide book around with him. It was our first walk around geothermal features and we found out about the rocks we could see: rhyolite (slow moving lava that’s cooled slowly and forms fantastic columns) and black obsidian (lava that’s cooled very quickly and becomes the black sand) and sinter (silica mineral dissolved out of the rhyolite by the hot springs): the cyanobacteria that lives in the hot pools and gives them their red, brown, green or blue colours: the lodge pine which thrives in the nutrient poor rhyolite soil and has evolved like many of the trees and plants to thrive where there are frequent forest fires.

Our final stop for the day was Old Faithful. Here the kids had to time one of its eruptions and use the data to predict the time of the next. If the current eruption is less than 2.5 minutes, the next eruption should happen about 65 minutes after its start: if it’s more than 2.5 minutes, you’ve got a 90 minute wait. Our prediction was 4:16; the Rangers’ was 4:15 and it actually started at 4:14. How cool is that!

*Geologically, Yellowstone sits on top of a “hot spot”. This is an area of light, hot rock closer to the earth’s surface than usual that produces the incredible hot springs, geysers and mud pools as well as the odd volcanic eruption. The last super eruption, around 630,000 years ago is estimated to have produced 60 times more material than the Krakatau eruption and 1,000 times Mount St Helens. The dust and ash covered around 2/3 of the US mainland and the explosion was so violent that it was followed by the collapse of the earth’s crust into a bowl shaped crater called a caldera (Spanish for cauldron) that is 30-45 miles across. The region is by no means stable now: there has been a number of smaller volcanic lava flows, and the roads are in constant need of repair because of earthquakes and the caldera floor’s constant movement – currently upwards at about 3 inches a year.

Ecologically, the variety of Yellowstone’s animal species is now similar to that of 2,000 years ago – but it almost wasn’t. By the end of the 19th century, America’s last remaining herd of bison roamed Yellowstone Park and their numbers had dwindled to 50 by 1898 and 23 by 1902. Although Yellowstone was declared a national park in 1872, no one enforced its conservation until the Cavalry was despatched to run the Park in 1886 which they did for 30 years till the National Park Service took over in 1918. Even then the policy regarding wildlife has changed direction like a pinball: there was a time when bears were encouraged to eat the hotels’ garbage and special viewing places were set up for tourists, now you aren’t allowed within 100 yards of a bear or wolf and feeding them is definitely not allowed.