Sleeping Tree Camp is another giant dwelling along with their mammoths found in the Whiterun plains just slightly west of the Western Watchtower. There is a cave located in this camp that has a quest involving Ysolda from Whiterun. Just be prepared to fight the giant within it if your stealth ability isn’t up to par to bypass him.
Naturally this is another spot where the mammoths don’t always stay on the ground.
Back to the theory of what goes up must come down is another dead mammoth for easy looting.
The Sleeping Tree Camp is just behind the rocks where the poor mammoth is laying. In this screenshot is the mod, Purity II by Laast, that gives the water its frozen glassy look.
The tree shimmering with a purplish glow will let you harvest one Sleeping Tree Sap. You can come back after it resets to harvest another one but you can only get one per visit. Don’t linger too long in the camp if the giants are alive because they don’t take like it and will attack should you get within range.
If you complete the quest for Ysolda, she will buy any Sleeping Tree Sap potions you find. This particular drug is legal in Skyrim so if you don’t like Ysolda’s price for buying it from you, the Khajits are known to pay a better price for this drug. There is always the third option, which is to keep it for yourself to use.
There are mods that modify the sap if you choose to use it and Herbal Tea by GustavL has a crafting ability to make Sap Solution. It requires 2 Sleeping Tree Saps and garlic for a bowl of food that gives you water-breathing and health regeneration.