Scott was pointing out some of the Canyon features to her. “…The peak over there is Mount Sinyala.” A crude cylindrical plug, with a flared skirt of smashed rock. “The channel that lies between Sinyala and these pinnacles in the foreground is the Colorado itself. The plateau you can see at the foot of Sinyala is called the Esplanade.” A cracked and shattered sheet. “It’s an erosional feature resting on one of the more resistant members of what we call the Supai Group of rocks. You can clearly see the contact between the Coconino Sandstone — that’s the lighter coloured stuff on top — and the Hermit Shale, the deeper red below.”

“Yes.”

“This is the western end of the Canyon. We’re a goodly way away from where the tourists come to roost, at the resort areas on the South Rim some way to the east of here. The landscape here is different. Older.” He pointed. “You can see cinder cones over here. Lava cascades.” He looked at her. “You know, you can tell the nature of the rocks, just by looking, just from the way they have eroded. The shales form slopes. The thick beds of limestone and sandstone form steep, almost vertical cliffs. And the Inner Gorge, at the very base of the Canyon, is a V-shaped groove that reaches down maybe a thousand feet to the river itself. Those are ancient rocks, igneous and metamorphic…”

She could see, now he described it, how the Canyon was a complex structure, channel cut within channel, Canyon within Canyon, each inner valley chiselled into harder, older rocks, all of it centred on the Inner Gorge, the narrowest valley cut into the oldest rock of all.

“Enough of the tourist stuff.” Now it was Monica’s turn to point. “Tell me about that.”

It was a plume of black smoke, rising from one of the incised channels.

Scott grinned. “You can see for yourself. One of those old cinder cones has just cracked open and started belching ash. We think a more significant event is on the way. We’ve recorded more seismic activity in the Canyon area in the last few weeks than in the previous couple of years. It’s actually very exciting; there are a couple of dozen guys from the Survey working the area right now…”

She let him run on. Right now the Administration was keen to keep enthusing scientists off the screens, but if this kid’s excitement was what motivated him to be up here and keep working and studying and gathering data, that was fine by her. The fact that what he was studying was liable to kill him, ultimately, was neither here nor there.