This sentence can be classified as a nonrestrictivephrase based on its composition and function in the sentence.
<h3>What is the difference between a clause and a phrase?</h3>
Clauses often include a subject and a verb while phrases do not. Based on this the underlined part is a phrase.
<h3>What is nonrestrictive?</h3>
This word is used when an element in a sentence is not essential to its meaning. This occurs with "formed by..." because this is only an extradetail about the canyon.