UN 10060 12/13
6.55mi RT, 2200' EVG
The Laramie-Poudre Tunnel is a water diversion tunnel finished in 1911 that connects the higher Laramie River to the Cache la Poudre River by traveling over 11,000 horizontal feet and about 1000 feet under the ground surface at its deepest point. Water is not sent through the tunnel during the winter months, allowing for an interesting journey underneath Green Ridge provided that you are willing to get a little wet.
We began at the pullout at Tunnel Creek along CO 14, where Joe(who had ventured through the tunnel before) led Nick and I up to the outlet of the tunnel. We decided earlier that it would be better to climb across Green Ridge to visit 10060 before dropping to the Laramie River and the inlet of tunnel instead of going through the tunnel first. We climbed over the talus pile near the exit and made our way up the steep slope to the edge of the trees. When we reached the forest the slope flattened out a bit and the snow deepened to about a foot in some places. We came up the side of the easternmost 10000' contour and climbed to the overlook. The view was impressive down to the river and across to the snowy peaks of the nearby ranges.
The summit contour is near the overlook, so we headed west a few minutes to climb to the less than obvious highpoint. The summit boulder had a small cairn on it and a register placed in 2008, though it was beginning to fall apart. After lunch we dropped off the summit and continued through deepening snow to the Green Ridge road and the edge of the ridge. Joe suggested following down a small drainage which took us down to the valley bottom, where we followed the winter road to the tunnel inlet canal. At the entrance to the tunnel we took a break to gear up for the dark watery journey ahead.
The inlet of the tunnel drops shortly through the first set of support structures to the gradual channel chipped through the rock. Most of the tunnel is a rectangular cut through the bare granite of the mountain with a rocky invert that collected a small stream of water about ankle deep in most places. Along sections of the tunnel it crosses small faults and joints spaced close enough together to require support sections, which were quite varying in design. Some sections were lined with railroad ties creating a box structure, in other places there were ties lined to create a long barrel staves along with other arches and tube structures spread throughout the tunnel. For the most part the supports were located a few thousand feet inward from both entrances where the rock is more fractured, the middle reach of the tunnel were mostly long bald sections with short supports every so often.
Directly downstream of most of the supports are pools that formed when the restricted cross-sectional area through the supports increases the water velocity, which is transferred to an increase in pressure when the flow area increases at the exit of the support. The pressure slowly wears away at the tunnel floor outside of the supports, aided by abrasive sediments travelling in the water. In most cases the pools can be crossed by staying to the sides of the tunnel walls where the water is only calf deep, but some pools at the invert of longer support tubes were thigh deep. In one pool we observed a small colony of brook trout who will be enjoying their little dark pool until the water flows again in the spring.
The water in the middle of the tunnel remains at a constant geothermal temperature of about 50 degrees, except near the entrances where cold groundwater enters the tunnel. When the groundwater carries dissolved ions, calcium carbonate soda straw formations grow as the water drips down the hollow tube. White fungi and molds grow in parts of the tunnel, especially in cavities near the timber supports. Along the length of the tunnel there were stationing markers each 100 feet that made it easy to track progress under the mountain. Faint reflections of light from the entrances can been seen throughout the tunnel, and the echoes of running water and kicking over rocks would rumble through the rock.
Overall the tunnel was a very unusual experience that I was glad to have, and thankfully everything went as planned. The tunnel seemed very safe, the worst danger would be hypothermia from exiting the tunnel with wet feet(which is why it was nice to start at the west entrance and exit only a few minutes away from the car. As long as you're sure the water is off for the season and you have plenty of light sources and batteries, I'd say that underground travel is just as safe as overground travel if you know what to expect. Thanks to Joe for organizing the trip and leading us through the tunnel, he has additional pictures of his two trips here and a history of the tunnel here.
The Laramie-Poudre Tunnel is a water diversion tunnel finished in 1911 that connects the higher Laramie River to the Cache la Poudre River by traveling over 11,000 horizontal feet and about 1000 feet under the ground surface at its deepest point. Water is not sent through the tunnel during the winter months, allowing for an interesting journey underneath Green Ridge provided that you are willing to get a little wet.
We began at the pullout at Tunnel Creek along CO 14, where Joe(who had ventured through the tunnel before) led Nick and I up to the outlet of the tunnel. We decided earlier that it would be better to climb across Green Ridge to visit 10060 before dropping to the Laramie River and the inlet of tunnel instead of going through the tunnel first. We climbed over the talus pile near the exit and made our way up the steep slope to the edge of the trees. When we reached the forest the slope flattened out a bit and the snow deepened to about a foot in some places. We came up the side of the easternmost 10000' contour and climbed to the overlook. The view was impressive down to the river and across to the snowy peaks of the nearby ranges.
The summit contour is near the overlook, so we headed west a few minutes to climb to the less than obvious highpoint. The summit boulder had a small cairn on it and a register placed in 2008, though it was beginning to fall apart. After lunch we dropped off the summit and continued through deepening snow to the Green Ridge road and the edge of the ridge. Joe suggested following down a small drainage which took us down to the valley bottom, where we followed the winter road to the tunnel inlet canal. At the entrance to the tunnel we took a break to gear up for the dark watery journey ahead.
The inlet of the tunnel drops shortly through the first set of support structures to the gradual channel chipped through the rock. Most of the tunnel is a rectangular cut through the bare granite of the mountain with a rocky invert that collected a small stream of water about ankle deep in most places. Along sections of the tunnel it crosses small faults and joints spaced close enough together to require support sections, which were quite varying in design. Some sections were lined with railroad ties creating a box structure, in other places there were ties lined to create a long barrel staves along with other arches and tube structures spread throughout the tunnel. For the most part the supports were located a few thousand feet inward from both entrances where the rock is more fractured, the middle reach of the tunnel were mostly long bald sections with short supports every so often.
Directly downstream of most of the supports are pools that formed when the restricted cross-sectional area through the supports increases the water velocity, which is transferred to an increase in pressure when the flow area increases at the exit of the support. The pressure slowly wears away at the tunnel floor outside of the supports, aided by abrasive sediments travelling in the water. In most cases the pools can be crossed by staying to the sides of the tunnel walls where the water is only calf deep, but some pools at the invert of longer support tubes were thigh deep. In one pool we observed a small colony of brook trout who will be enjoying their little dark pool until the water flows again in the spring.
The water in the middle of the tunnel remains at a constant geothermal temperature of about 50 degrees, except near the entrances where cold groundwater enters the tunnel. When the groundwater carries dissolved ions, calcium carbonate soda straw formations grow as the water drips down the hollow tube. White fungi and molds grow in parts of the tunnel, especially in cavities near the timber supports. Along the length of the tunnel there were stationing markers each 100 feet that made it easy to track progress under the mountain. Faint reflections of light from the entrances can been seen throughout the tunnel, and the echoes of running water and kicking over rocks would rumble through the rock.
Overall the tunnel was a very unusual experience that I was glad to have, and thankfully everything went as planned. The tunnel seemed very safe, the worst danger would be hypothermia from exiting the tunnel with wet feet(which is why it was nice to start at the west entrance and exit only a few minutes away from the car. As long as you're sure the water is off for the season and you have plenty of light sources and batteries, I'd say that underground travel is just as safe as overground travel if you know what to expect. Thanks to Joe for organizing the trip and leading us through the tunnel, he has additional pictures of his two trips here and a history of the tunnel here.
