It is either a valve or a natural gas site for locators to access the locate wire. The color yellow is the code color for natural gas. I am by profession an underground lines locator. Before you dig dial 811.
Thanks for the warning! Having, when I was a plumber, chopped though a Telecom cable the size of my thumb I know where you are coming from.
Yeah buddy. Excavators hit my underground lines and say my marks were off. Uh, no you pal you moved it overr. And then I tell them in a polite manner that I have before pictures like the ones here.
Dean Whitehorn 
I see these when I am out running and wonder exactly what they mean. Then they eventually fade. The colors must mean something too.
Probably utility location prior to earth works.
It is either a valve or a natural gas site for locators to access the locate wire. The color yellow is the code color for natural gas. I am by profession an underground lines locator. Before you dig dial 811.
Thanks for the warning! Having, when I was a plumber, chopped though a Telecom cable the size of my thumb I know where you are coming from.
Yeah buddy. Excavators hit my underground lines and say my marks were off. Uh, no you pal you moved it overr. And then I tell them in a polite manner that I have before pictures like the ones here.