What Are the Circular Plaques Along the Los Gatos Creek Trail?

Ever since Mimi and Robert Melnick published Manhole Covers of Los Angeles in 1974, covers have been recognized as works of art, cast metal sculptures, like coins.

They are a bit hard to hang on the wall, but people have collected them by making rubbings and pictures. An art class at San Jose State painted the covers on campus. The colored covers of Tokyo are famous for their beauty. There are now several Internet sites with pictures of manhole covers from all over the world.

All through my career in Public Works Sanitary Sewer Engineering I made photos of the amazing variety of manhole covers in San Jose.

Everywhere we went on vacation, I collected pictures. While everyone was watching Old Faithful erupting, I was over by the ranger's office collecting a manhole cover picture.

In Yosemite, my trained nose lead me out into the middle of a large meadow to a NPS cover. I have one from Moss Landing with a hydrogen sulfide warning on it. I made a special trip when I saw it pictured in an engineering magazine. I always have an eye out for them.

On a bike ride along Los Gatos Creek Trail in late September, between Highway 85 and Vasona Dam, I spotted what looked like three new manhole covers that turned out to be works of art, not covering any utility openings.

Same size and shape, but just for looks. There was no evidence of new sewer pipe construction. I got off to take a closer look. They are about the size of manhole covers, but they are not cast iron, there is no ring, they are cast concrete and at least four-inches thick.

Each has a simple substitution cipher message on it and each has a key, making deciphering very easy. I won’t spoil your fun by solving the cipher. Once you figure out how the equation defines the letter substitution, you can read it while standing there.  

I went several miles on either side and did not find any more. The pictures of the plaques included with this article are for your enjoyment and edification.

First let's look at a common West Valley Sanitation District, Los Gatos Creek Trunk Sewer cover. This is the real deal, about two feet in diameter, about an inch and a half thick, cast iron, weighing about 150 pounds. It is marked S for Sanitary.

Sanitary sewers are very unsanitary. Storm drains are marked D. This is an older one, made in Santa Clara. Now days, most are made in Mexico, India or China. This is more artistic than most, because it's been spray painted green. This is only one of several patterns that you may find in WVSD, even on this one trunk sewer. Notice that it sits inside a cast iron ring. It has a pick hole and notches to facilitate removal.

Now let's look at the recent arrivals. Going north to south, the first one is just south of Highway 85, on the east side of the Creek. Put the coordinates 37.2566, -121.961905 in the Google map search window and zoom in to see the location. 

Looking south, you can see Highway 85 on the right edge of the picture. There is already a welded sculpture and a bench in this location. Notice the notches in the edge and the piece of chalk in the one to the left. There is a connect-the-dots skeleton picture in the center that someone has drawn in and that has been partly worn off.

It seems to be cast cement, with a ring of metal bolt heads sticking out of it. The key to the cipher is below the skeleton, x=y. I kicked the dirt away from the edge. There is no rim, no pick hole, no notches. It doesn't sit in a frame, it is simply a disk set in the ground, and I went down only about four inches.

I don't know how thick it is or whether it is anchored in some way. I wondered whether someone might steal them. They look to be pretty heavy.

The next one is a little farther north on the same side of the creek, at coordinates 37.253939, -121.963214. In the picture it is in the shade between my bike and the bench. I always keep an eye out here because there is a storm cover that sometimes pops off in major rainstorms and I kick it back into the frame to keep anyone from going down.

There is nothing worse than stepping on a loose cover, having it give way and drop you into the hole, and coming around and whacking you as you go down. But this one is on the wrong side of the bench, never been one here before, no pipe below it.

This one has a ring of hex bolts in the center, one missing, with the cipher equation in the center. A somewhat fanciful alphabet, but not too hard to make out. Was this put here by aliens? This one was cut into the bank. Recent rains have eroded dirt onto the top, partly covering the cipher.

The next one is south of the bridge at Lark Avenue, on the east side of the Creek, at coordinates 37.251081, -121.965021. You can see that it is right under the power lines and next to a bench.

On this one numbers represent the letters. Again, a very simple code, with the key given in an equation.

I looked online and couldn't find out anything about them. I contacted Santa Clara County Parks, Water District, Town of Los Gatos, Los Gatos Patch, Los Gatos Weekly Times, and Los Gatos Museums. No one knew anything about them, who put them there or what is their purpose. I found other photos of one of them online.

Somebody has been replacing the chalk. I hope to catch them some day. I would like to talk to them about these "manhole covers." Art imitates life. 

Editor's Note: Los Gatos Patch reader Gary Hinze wrote this guest article for us on the enigma of the plaques found along the Los Gatos Creek Trail. He became as intrigued by them as we were after we posted a story on the site asking what they were. That question was prompted by a reader who posted a photo of one of the plaques in our pics and clips area of the website.