Looks alot like a fungus I found in one of my gardens near where an ash stump is rotting away. Creepy cool stuff. If no one who knows chimes in my GUESS is there is something, possibly your tree's trunk, rotting under the gunk.

Perhaps root initials?
Never saw that when I lived in SoCal.

This will really seem like a dumb-**s statement, but I have to ask, these trees likely don't have pests affecting them though? These trees "oils" are used for pest control, right? I have seen on the show"Billy the exterminator", that these trees have an oil that is really popular, and affective in getting rid of many pests, without harming people. It is a warm climate tree, but, this tree has been used in pest control, and has apparently been made available in the USA.