Perched for the last century on the sandstone facade of the First National Bank building here, three impish gargoyles have watched the changing foot traffic on Main Street, as this small plains city reinvented itself again and again.

When cattle was king, this proud building of Romanesque arches was the headquarters of a vast cattle and land empire. When coal was king, the back offices became a health clinic for the United Mine Workers of America.

With tourism now the king in Colorado, the former union clinic receives medical travelers from around the world who have come to consult a surgeon who has made this town known as ''the sex-change capital of the world.''

''It's a boon to business here,'' the surgeon, Stanley H. Biber, said of his specialty in this town 200 miles south of Denver. ''They come with families, they stay in the hotels, they eat in the restaurants, they buy at the florists.''