Okay who knows what the goo is on the thread of your tires. Seems to occur after riding through puddles in the winter. This isn't mud, it's slimy and won't wash off.

I get it a lot on Gibbs Lake trail, there I chocked it up to the big green slugs. Run over a few of these and your tires are picking up sticks, leaves, rocks and small rodents.

Okay who knows what the goo is on the thread of your tires. Seems to occur after riding through puddles in the winter. This isn't mud, it's slimy and won't wash off.

I get it a lot on Gibbs Lake trail, there I chocked it up to the big green slugs. Run over a few of these and your tires are picking up sticks, leaves, rocks and small rodents.

horse poo?

horse poo?
After further study of this particular phenomena, I fear you’re right :(

you must have ran one of these over. With no concern for it's family!
<img src=http://www.gi.alaska.edu/~jesse/treasure/happycamp/slug.jpg>