This cache is placed in the Perminente creekbed, in a very interesting section of the waterway where the creek passes under the the Cuesta/Miramonte intersection. The cache is small, with room for some trinkets, and a logbook and pen. You can access it by standing on top of the sandbag 'dam'. You don't need to enter the tunnel, or go on or under the road in any way. Please place the cache back exactly as you found it, and sign both the physical and electronic logbooks.
A huge congratulations to Chet13 for spending a literal hour getting FTF.