According to GORP (not the be confused with The World According to Garp), the mountain biking website, a little over a hundred years ago, Bob Waterman and his bride visited the Arroyo Seco Canyon and spent their honeymoon hacking a trail that their horses could use. They returned and told a Los Angeles carpenter, Perry"Commodore" Switzer, about the beauty of the canyon. Switzer improved and expanded the trail and built Switzerland, the first resort in the San Gabriels.
Access into the canyon was by horse, stage or foot until the early 1920s, when the lower canyon was paved. Later, during the Depression, the construction of the Angeles Crest Highway allowed motorists to reach many parts of the upper canyon. Then the great flood of 1938 destroyed most of the paved road and the structures in the Arroyo.
You begin your journey at the corner of Ventura Ave. and Windsor St. in West Altadena. You can park in the paved lot immediately west of this intersection (or on nearby side streets). There are two paved roads leading north into the canyon. The left (west) one descends into the parking lot of Cal Tech's Jet Propulsion Laboratory. You enter the road to the right (east) by riding around a locked yellow gate.
In light of all the other wonderful caches in the Arroyo [of all the ones I originally listed, only Rock 'n Row remains], I am just building on the foundation of those who came before.And enjoy a whole lot of new ones put out since since Thanksgiving 2005 by PackerTrekkers [wow, that's an old note]
In fact, it is a miracle that this location was not yet used as a cache site. The Gorp site says that this in the largest man-made structure in the Arroyo. That is a dubious assertion, but the stucture's name and redundant warning sign make it whimsical.
Note: The cache is not off the trail and you do not need to descend into the (former) streambed or go on to posted or fenced-off land to find it. Assume that reception is difficult under the tree cover.
Back in action thanks to the kind efforts of Kelsoboom. Much obliged, sir!