Please see picture.

Mine looks like this too. I think it’s because of the difference in the depth of soil (the brown areas are over ledge) and also exposure to scorching sun. In the spring and fall they are uniformly green.

St. Augustine

While what has been said is valid there may be another reason the grass is greener, and that is the stratigraphical structure of the yard. In my yard there is a porous lay that runs down the hill. When we planted a tree, I would fill the basin around the new tree, and a few minutes later the water would come out of the ground a dozen feet down the slope. There was no evidence of water on the surface between the tree and the wet area.

Old pits or trenches will cause the same effect. Water collects in the now filled in pit and keeps the available moisture in that part of the yard higher than other parts. When many homes were constructed; a hole was dug and filled with construction rubble. It was then filled in. The landscaper may not have know it existed by the time he was there to do his job.

This same effect is used in Archeological dig to screen for old building and other formations that are not visible on the surface. This can be seen by the greener lines or blocks in the fields,

Do you have an unknown pipe or line leaking in that part of the yard?

@krnuttle, no leaks as far as I know.  I've shut the water off from the house and the meter stops moving.

That REALLY looks like a leaking pipe. Been there before.

Where do you live?

Do you have an in-ground watering system or do you use a hose and sprinkler?

What is your watering schedule? How often and for how long do you water?

Is the dry area next to a west facing wall or fence?

I may have found the problem. I think the area in the pic is much greener and taller because the sprinkler head sunk below ground level and the water was just spraying out and in the green area only. I went ahead and raised the head and now it sprays out and over the grass all the way around.