The Endless Tunnels
Dani and I weren't actually looking for a tunnel this weekend (although, admittedly, we had a few in mind for later in the day).  However, we stumbled across this promising-looking one and, as always, had our boots and gear handy.  This turned out to be a really terrific system of several tunnels, among the longest we have gone through... as my sore muscles presently remind me!
The entrance here is actually three tunnels of this size (the third was cropped, sorry!) which all empty into a canal running next to a Wal-mart shopping center.  The smaller tunnels near the right side of this picture presumably drains the parking lot and/or street beyond.
The first tunnel we explored was the one I was standing by in the photo above.  The individual corridors were more or less straight, but there were numerous "dog legs" throughout, which did at least keep things interesting.  There was relatively little debris or mud throughout the entire system and only a few side tunnels to feel into this one.
After the luxury of the 8 ft. ceiling, this part of the tunnel raised the floor up to approximately a six foot overhead.  On these occasions I am somewhat thankful for my average stature.
Here is another of the twists in the path.  Note that the floor is dry where I am standing.  This was typical in several parts of the system.  I started paying attention to this after spotting wet footprints preceding us in another tunnel some months back and have therefore begun staying alert to the possibility of encountering humans where one would not typically expect to find them!
This is an isolated patch of mold, not to be found anywhere else in this system.  Though it superficially appears to be rusty water, there was no metal nearby that would account for this volume of this stuff.

I have run across this type of fungus (I presume) a few times before in our explorations, but I have never identified it.  In particular I remember seeing it in drains in my childhood (I'm sure Freud would have much to say on this statement).
The exit, at last!  The tunnel finally opened into a paved conduit (if that's the right word) at the bottom of an incline.  To the right as you exit is an apartment complex.

Just a short distance (531 ft.) beyond the exit was another tunnel.  Needless to say, the numerous apartment denizens getting in and out of their cars had some funny looks for us as we proceeded toward the next tunnel.

GPS coordinates of this tunnel's end:
32.65907 N, -97.40454 W

Approx. total distance:
0.54 miles (2851 feet)
I have to admit that I was skeptical that we would pick up on a new tunnel after going so far in the previous one, but this turned out to be a really interesting part of the system after all.

And note the trees to either side that have been ravaged by beavers.  Yes, beavers! (more on this later...)

GPS coordinates:
32.65738 N, -97.40310 W
On to the next part