The third of three etchings Smillie did of an event he witnessed in Yosemite in 1871 and wrote about in Picturesque America. This image is based on a drawing he did for the publication, illustrated on page 482.
'There were no saddles; the riders...rode with only a sheepskin or a bit of blanket under them...The word was given; the horses plunged, started, 'bucked';...An unlimited amount of profanity expressed the impatience of the crowd...At last they came...a cloud of dust, rattling hoofs, and frantic riders plying their whips...the crowd capering, screaming and 'hollerin' like so many madmen.'"
The horse races were wagered on heavily and the riders were tied to the horses which could be fatal if a horse stumbled. Note that the last rider in the group appears to be the artist.