Landships II

It's a steam tractor by Daniel Best's company - Best later merged with Holt to form Caterpillar. The photo appears on this page:

http://haskey.com/johnh/steam/best/best_tractor.html

It seems to be a 1905 model, and according to that site, the photo you found was published in 'Railroad magazine', part of the caption reading:

Alex Isgreen was the engineer, Jerome Connelly the fireman, and Walter Saunders did the braking. Mrs. Saunders and Belle Hutchinson kept a sharp lookout for Gila Monsters.

Ah, those were the days...

It would appear that there's at least one example of the tractor still in running order at the Oakland Museum. There are loads of absolutely fantastic photos of it in action here (note the smoke stack with spark catcher - clearly a wood burner):

http://railway.gwernol.com/SPCRR_05/best.htm