Persistent Dry Circle in Gravel Driveway

Is it about the size of a manhole?

Yes, approximately 29 inches in diameter. This is well inside my yard. No street sewers underneath.

Was there a well once on your land, in that spot?

I'm guessing, because of the perfect circle, that it is or was some form of man made aperture.
The sewers or drainage could have vented there years ago, or had an inspection hole, but have since been re-routed and capped, but still affects the temperature or drainage of the land surface, the way manholes nearly always melt the snow which lands on them, whilst the surrounding road turns white.

I believe you are right, especially with regard to temperature. We're going to have to dig that baby up for confirmation.

No well, anywhere on the place. I've lived here 45 years. They already had city water piped in, when I came. A street sewer line wouldn't make sense in this location. It would have to be at a 90 degree angle to the street, and lead nowhere. There are and were no streets or houses in that direction, only open, undeveloped land. I probed the soil with steel rods. Nothing found. Even tested the electrical resistance of the soil with the rods. It was high; characteristic of soil, not of pipes, sewer or well covers.
If something manmade is buried at this spot, I have to ask myself, why did the circle appear only a month ago.
There is another problem--- One day the gravel got a good soaking. The same circular area now retained moisture, even when the rest of the drive had dried, reversing its former behavior. In a few days it had returned to its usual persistently dry status.

Some types of fungus grow in circular patterns, but they are rarely perfect circles. Can you manifest it by spraying the area with a hose?

If it returns, try to get some photo's at various angles and some closeups of the ground.

My best guess (and it's just a guess) is that some type of barrel or container was placed on the ground (and later moved) and it had some type of chemical on it which remained on the gravel.

This interests me as well.

No containers or chemicals placed on the gravel. I would remember if this had been done, as the circle only appeared on Jan. 4th, just over a month ago.

I've heard of fungus rings that grow underground and harm the growth of plants. There are no plants in this case, merely the gravel. I've heard, too, that fungus rings expand from the center, making larger and larger rings. This business on my gravel is a solid circle, not a ring, and it's stayed the same size for over a month.

How long has this circle been around?

-- pun only partly intended --

Is it possible that some container was placed there a long time ago and left some residue and the circle effect only appears under certain conditions (which just happened to occur recently)?

Other than that, I'm running out of ideas. Finally we would need more data, like photo's and/or soil (gravel) samples I think. Also, what type of environment are we talking about here? North, South, East, West, Hot, Cold, City, Country, Rainy, Arid? Are there kids around? Kids (and teenagers) can leave all kinds of strange things either by accident or through mischief.

It was seen nearly every day for about a month. Heavy rains have left it invisible for the past few days, as all of the gravel is thoroughly soaked. The dry gravel circle appeared in a larger area of gravel that was dampened by morning dew. It appears to be able to dispense with light dampening only. Once the storms pass, perhaps it will reappear.

"Some types of fungus grow in circular patterns, but they are rarely perfect circles."

Yes, I've always known this (as well as the circle of mushrooms) as fairy circles. These (usually) grow on places where old tree stumps were, I thought.

I'm thinking latent entrance to hell.

I've lived here for 45 years. No recollection of anything placed on the gravel at any time, that might explain this phenomenon.
There doesn't appear to be anything particularly unusual about the current conditions. January and the first week of February was mostly rain-free. Cool nights, mild days, most cloudy, a few sunny. Typical between-storm winter weather here in Northern California. The last few days have seen moderately heavy rain. The current conditions have occurred many times before, without the the dry gravel circle ever appearing.
I live alone here, so something done without my knowledge is very unlikely. The gravel drive is inside a fenced yard, with the gates locked at night, and when I'm away. The chances of contamination of the gravel with something causing the drying seem low.
I tried a little experiment, wherein I took samples of the gravel from the dry area and placed them within areas that were normally damp with dew in the morning. The samples soon began to dampen like the gravel that surrounded them, and unlike the gravel in the circle. I strongly suspect that the location of the dry gravel circle, rather than the gravel itself, or anything on it, is the key to the phenomenon.

Probably not that ; ) . I measured the soil temperature in the circle repeatedly and found it slightly below that of the other parts of the driveway.

You don't happen to live in an area that's prone to sink holes, do you?

Usually it's a limestone thing.

Having a different temperature still leads me to think that there's some sort of hole down there, which keeps a constant temperature a bit like a submerged cellar.

You could do with having a quick turn on one of these.....




The soil sampler......not the girl.

are you in an area that is underlain by the corchoran clays?. These are caliche type deposits that often act like hard limestone beds. You may have a little "sinkhole" developing because the clay has been punched through a bit.
See if there's any airphoto evidence of other nearby areas that show similar properties.