Plaza de Mulas is one of the largest high-altitude base camps in the world: a temporary town of tents at about 4,300 metres, on the long valley route to the summit of Aconcagua. It exists only because the mountain is there. Everything in it arrives on the back of a mule — food, fuel, timber, the tents themselves. Arrieros bring the loads up and take them down. A cook feeds the camp out of a dome. Climbers walk in for days, pitch among the rock, eat, wait for weather, and walk out again. The mountain does not notice. This is a book about that town: a brief, warm, human occupation at the edge of an indifferent geology, and the labour that holds it up.

I photographed it with two cameras at once.

The slow half is black-and-white, on a 4×5" field camera, one sheet at a time. A large negative holds a wall, a ledge, the grain of old ice — and it holds a face at altitude with the same weight it gives a mountain. I use it for what stays: the range, the penitentes, the night turning over the camp in star trails, and the people who live and work up there — the man at the table in the dome, the man among the cargo, the arriero at the rail.

The quick half is colour, on a small rangefinder I carry like a diary. Warm where the mountain is cold: red and yellow dome fabric, a pot on a stove, a tent door framing a peak, snow settling on the skin of a tent. It is for what passes.

I did not go for the summit. I went for the camp.