If Joseph Smith had been writing the Book of Mormon instead of translating it from ancient records, he would have been very foolish to have included references to horses on the American continent in Book of Mormon times. (1 Nephi 18:25; Enos 21.) In 1830, nearly all the historians and scholars were convinced there had been no horses on the American continent before the coming of Columbus.
After the Book of Mormon was published, however, archaeological discoveries were made that clearly indicate that horses were in the Americas before Columbus arrived. In the asphalt deposits of Rancho LaBrea in southern California, numerous fossil remains of horses have been found that antedate Book of Mormon times.
Although these discoveries do not absolutely prove horses were in the Americas in the time period covered by the Book of Mormon (about 2600B.C. to A.D. 421), they do prove horses were there before the coming of Columbus” (Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 117).
(Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 117)