I found this photo on Flickr and the comment below it by 'fogdrip' indicates that it is a water collection tunnel for Henninger Flats. I've never seen or heard of these and was wondering if anyone has any info on them. The description of the photo indicates it is near the Idlehour Trail junction with the Mt. Wilson Toll Road.
I've seen quite a few of these around. At Brennen's slide show he mentioned one that people used to crawl through in Eaton Canyon that they've since destroyed.
