I saw a similar cache to this somewhere and it made me laugh and laugh and laugh. It reminded me of one of my true loves - the mule! The cache is placed so you can view probably one of the biggest mule herds in Nebraska. If you whistle or hollar 'someone' will probably come check you out.
A mule is the offspring of a male donkey (jack) and a female horse (mare). Horses and donkeys are different species, with different numbers of chromosomes.The size of a mule and work to which it is put depends largely on the breeding of the mule's dam. Mules can be lightweight, medium weight, or even, when produced from draft horse mares, of moderately heavy weight.
It has been claimed that mules are "more patient, sure-footed, hardy and long-lived than horses, and they are considered less obstinate, faster, and more intelligent than donkeys." There is of course the rumor that the mule is stubborn. Which you may just need to be to solve this puzzle cache.