Why does Of Mice and Men start and end with a scene of nature?

It starts and ends in the salinas river.I can't figure out why.I have my GCSE literature exam coming up soon and I thought it would be useful to know.Why does Of Mice and Men start and end with a scene of nature?
Steinbeck grew up in the Salinas Valley region of California, a culturally diverse place of rich migratory and immigrant history. This upbringing imparted a regionalistic flavor to his writing, giving many of his works a distinct sense of place.





that might have had something to do with it.Why does Of Mice and Men start and end with a scene of nature?
It is the symbol of the wheel of life. Sometimes people die the day they were born creating a circle. Also nature has a great importance in Literature because it reflects human moods.
maybe because it's very dry there and the river is a sign of life, refreshment...
i dunno lol