I took some time to look around and unfortunately can’t figure out which model this is but diesels in Cat products were very common back then. This one is definitely diesel since it has an injection pump and a 3 cyl engine as there are three injector lines. Cat made some gas stuff but by the middle of the '30s they made half of all the diesel power in the US.

The wide low ground pressure treads with a special grouser profile on the trackpads make this machine suitable to work the type of ground described. I would like to see the PTO arrangement on the front that powers those chains to lift that heavy booger of an implement.

In reply to Mark P, it is a Cat RD6 diesel. Three cylinders with pistons the size of small coffee cans and eight inches of stroke. It was governed at about 800 RPM but did its best work down about 600 with the throttle wide open. It had enough raw grunt to affect the rotation of the earth if you had it pulling in the right direction. The only thing using gasoline was the two cylinder pony motor used to start the main engine. For many years around many mining and construction sites the morning quiet was shattered by the sharp cracking exhaust of unmuffled Caterpillar pony motors.

If we could transport the driver to today, he could attend a steampunk party and fit right in.

Before I enlarged the photo the springs that keep down force on the tool in the ground looked like hydraulic cylinders. Thinking it was early to see them. Further inspection shows the plough is moved by chains coming from the front of the machine. Possibly not even a diesel yet too. A friend of mine had a road grader on his property in Maine to service the miles long dirt road into his property. The machine was from about 1930 or so. A full size grader pretty much like you see today. It was powered by a four cylinder engine from a Model T. Back then it wasn't all brute power but more engineering and gearing. So much for the golf club carrying 600HP half ton pickups today.

[Here's a side view of this Caterpillar tractor. - Dave]