What is that black gooey stuff all over the ground at the park (NW Military side)? It looks like tar.

The black stuff all over the ground and sidewalks on the NW Military side of the park is the fruit from the Texas persimmon. The fruits start out green and ripen to a black color. The Texas persimmon is a native small tree all over the park. Wildlife including birds and raccoons depend on the tasty fruit when very little else is out there to eat.