Did some draining a while back, I managed to map out the drain path by popping out into side tunnels where the main pipe connected to the street and got a gps signal. All told I went about .75 miles down the main drain with no sign of it stopping! I plan to go back in the winter when theres less water to find the end.

Pro tip, use a skateboard to glide down those narrow tunnels.

https://imgur.com/a/2zVsFKF

Nice pictures!

I've often thought about using a skateboard or long-board to explore some of the narrower tunnels here as well!

Great photos! I'd love to make it up there to explore these drains, I'm in Colorado Springs. There are some good drains here, but they tend to be pretty short, most of the drainage here is just canals and creeks, as well as drains to small for me to want to explore.