Tumbleweeds conjure images of the Old West, rolling through desolate towns as twisted balls of dead foliage. But while a staple of Western films, they are an unusual sight in 21st-century Utah.

Tumbleweed is sprawling across sidewalks. It is blowing across freeways. It is stacked up — feet high — against homes in Utah and Nevada. The masses upon masses of prickly tumbleweed are more ...