This sketch is suspected to be created around 1483 and it's believed that this ravine wasn't an actual place, but instead from Leonardo da Vinci's imagination.  The only way for Leonardo to have been able to create a realistic looking ravine without copying one he would have been looking at would be to study them extensively.  This has also been proven by some of his ideas about the actual age of the Earth. Although exceedingly controverisal, Leonardo believed the earth was much older than thought at the time because he studied different seashells found on mountain tops and theorized that they couldn't have been placed there.  Instead, water was one there and as time passed, the water levels decreased and fossils of bones were left in areas of higher elevation.  Leonardo also understood that this process wouldn't happen quickly, but slowly over long periods of time. Although there doesn't appear to be any shells in this image, the decrease in water level is clearly visible in this sketch.

Works Cited:

Jones, Johnathan. Leonardo Da Vinci's Earth-Shattering Insights about Geology. 23 Nov. 2011, www.theguardian.com/artanddesign/jonathanjonesblog/2011/nov/23/leonardo-....

Leonardo da Vinci [CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)]

“Leonardo Da Vinci (Vinci 1452-Amboise 1519) - A Ravine.” Royal Collection Trust, www.rct.uk/collection/912395/a-ravine.

Rosenberg, Gary D. The Revolution in Geology from the Renaissance to the Enlightenment.