Answer:
The sentence that is unrelated to the main idea is:
Located in the state of California in the Sierra Nevada Mountains, Yellowstone National Park is a perfect place to take a vacation.
Step-by-step explanation:
After reading the passage, it is easy to see that the main idea is related to the preservation and the conservation of certain areas in the country. However, the last sentence suddenly states that Yellowstone is a perfect place to take a vacation. Even though Yellowstone was mentioned in the previous sentence, it was still in connection with the same main idea. Now, out of the blue, the writer shifts focus from the importance of preserving certain areas to how enjoyable one of them is for the holidays. Having that in mind, we can say that the sentence which is unrelated to the main idea is:
Located in the state of California in the Sierra Nevada Mountains, Yellowstone National Park is a perfect place to take a vacation.