Mount St. Helens vs Mt. St. Helens

Mount St. Helens and Mt. St. Helens both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mount St. Helens	Yes	No	No	No
Mt. St. Helens	Yes	No	No	No

As nouns, Mount St. Helens and Mt. St. Helens are synonyms defined as:

Mount St. Helens and Mt. St. Helens: an active volcano in the Cascade Range in southwestern Washington; erupted violently in 1980 after 123 years of inactivity

Other synonyms of Mount St. Helens include Mount Saint Helens.

Mount St. Helens (noun)	Mt. St. Helens (noun)
an active volcano in the Cascade Range in southwestern Washington; erupted violently in 1980 after 123 years of inactivity	an active volcano in the Cascade Range in southwestern Washington; erupted violently in 1980 after 123 years of inactivity