This pine log was from a tree felled in the spring on a nearby property. The tree remained where it was felled, limbs and all still attached, to allow the moisture to be pulled out over the heat of the summer.
I read somewhere that felling a tree and leaving it whole, the tree will continue living so long as the leaves have moisture to draw from. With the tree on the ground the only water remaining is that which is left in the tree itself.
The blue denim color is the change in the sap color from being on the ground like that all summer long. If the tree was felled in the winter, the staining does not occur. At least that’s my understanding of it.