What kind of thistle do I have?

There are 3 main thistles in La Plata County. Scotch thistle is very big and spiny with large gray/green leaves and large purple flowers. Musk thistle is tall, but have darker and smaller green leaves/stems with symmetrical leaves. They have single pinkish/purple flower heads.  Canada thistle grows relatively shorter but in thicker stands, and have clustered seed heads with multiple, small pink flowers.  Canada thistle is prevalent near waterways, such as riversides, irrigation canals, fields and ponds, although it can also be found in dry sites.  Bull thistle has a unique leaf shape, which is narrow, spine-tipped, and progressively narrower at the tip.  The leaves are also dark green and have fine hairs.  Scotch, Musk, and Bull thistles are all biennial; meaning the first year the plant is a small rosette, without flowers.  The second year the plants produces seeds via flowers then die.  Canada is a perennial, meaning it lives year after year.