Were the mountains "calling" Muir?

Atop a 13,000-foot Sierra peak, I asked a group of hikers about John Muir. One of them mentioned Muir’s desire to protect nature. Another quoted Muir’s most famous line, “the mountains are calling and I must go!” But what did Muir really mean when he wrote that?

In 1873, Muir concluded a letter with, "The mountains are calling and I must go and I will work on while I can, studying incessantly." How do you think the meaning of the word "calling" changes after reading the whole sentence?

In the rest of the letter, Muir suggests that he is struggling with writing. Perhaps the "calling" mountains are an excuse to go for a hike and not to write. (John Muir Papers, Muir to his sister, 1873)