Answer:
The sentence "Arches National Park in Utah, where many western movies have been filmed, is filled with many natural stone arches." is correct as it is.
Step-by-step explanation:
The use of commas in this sentence is setting apart the irrelevant information about the subject which makes this sentence a composed sentence being "where many western movies have been filmed" a subordinated sentence since this could be removed from the complete statement and it would not affect the message.