The Thew model O steam shovel from about 1898, self propelled and steered (all others were limited to working from railroads)

Above from Shorpy

The color photos and write up are from http://www.mylargescale.com/Community/Forums/tabid/56/aff/8/aft/111626/afv/topic/Default.aspx

Back in the 1890s, Thew, captain of an ore-carrying boat on the Great Lakes, often encountered the problem of handling iron ore once it was deposited on the docks. At that time, such work was done with "railroad-type" steam shovels that traveled on railroad tracks. They were heavy, cumbersome, and could only swing their booms from side to side in a half-circle. Much hand work was required to clean areas beyond the shovel's reach and also to frequently reposition the railroad tracks.

Captain Thew studied these problems of ore handling and conceived a unique machine that would overcome the former difficulties and restrictions. With the help of H.H. Harris, an experienced shovel designer, Thew built his first machine at the Variety Iron Works in Cleveland in 1895. His machine was a fully revolving steam excavator with a 5/8-cubic-yard shovel attachment that could swing in a full circle, the first with this capability built in America. To add even more flexibility, he mounted the machine on four steel traction wheels, which could steer and propel itself without the need for labor-intensive rail tracks. Now able to travel without restriction, the shovel was able to perform any loading or cleanup work over the entire dock property, doing away with most of the hand labor