Scotch thistle
(Onopordum acanthium)
A biennial that was introduced from Europe or eastern Asia and can reach a height of eight feet. The rosette forms the first year and can have leaves up to two feet long and one-foot wide. The second year the plant produces flowers that are reddish-purple to violet.
It is found primarily along roadsides and railroads, but can become an impassable obstacle to livestock on rangeland and pastures. It’s common throughout the county, with the worst infestations found between Glenwood Springs and New Castle.