A mountain riddle is:

Q: How do mountains hear?
A: With mountaineers (mountain ears).

The joke was published in Biggest Riddle Book in the World (1976) by Joseph Rosenbloom.

“How do mountains see?"/"They peak” and “How do mountains stay warm?"/"Snowcaps” are related riddles.


Google Books
Biggest Riddle Book in the World
By Joseph Rosenbloom
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 35:
How do mountains hear?
With mountaineers.

Google Books
1976, Boys’ Life, pg. 9:
How do mountains hear? Answer: They have mountaineers.

Newspapers.com
16 June 1977, Emory County Progress (Castle Dale, UT), “Kid Stuff,” pg. 16, col. 1:
1. How do mountains here?
With mountaineers.

Google Groups: alt.humor.puns
Puns of the Weak 1-3-03
Stan Kegel
Jan 4, 2003, 12:59:25 AM
(...)
How do mountains hear?
With mountaineers. (Dave, 10)

Google Groups: alt.humor.puns
Kids Puns of the Weak 02-08-05
Stan Kegell
Feb 8, 2005, 3:12:20 PM
(...)
How do mountains hear?
With mountaineers. (Dave, 10)

Reddit—Sleuths
Posted by u/kevjumba June 21, 2012
How do mountains hear?
COMMENTS
[deleted]
Their range is excellent.
kevjumba
not quite but good try lol.

Reddit—Dadjokes
Posted by u/OthelolzNZ March 17, 2016
How do mountains see?
They peak.
COMMENTS
d_daggins
And how do mountains hear?
With mountaineers
jlhc55
How do mountains eat?
They gorge themselves.
positive_electron42
How do mountains stay classy?
With mountaintop hats.
piratius
How do mountains eat?
Off a tectonic plate!

Reddit—Jokes
Posted by u/beyonsay_what November 13, 2020
How do mountains hear?
with mountaineers (mountain ears)