Low mounding weed invading fields and pastures
It looks like small carpetgrass (also called jointhead grass). To be certain, can you pull up a plant and take a picture of it with a white background? Or, if you are close to the Extension Office (330 Montevue Lane, Frederick), you can drop off a sample.
If it is small carpetgrass, mowing will help to deter and control it. It is an annual, so once it sets seeds, that plant is done with its lifecycle. In order to reduce the number of seeds that could come up next year, it is important to prevent the existing plants from producing seeds, and mowing will certainly help with this.
Another option is to use a non-selective herbicide such as glyphosate. Small carpetgrass tends to grow in wetter areas. If you are using a herbicide and there is a body of water nearby, be sure to read the label for any instructions on distance to water.
You can read more about small carpetgrass on the Maryland Invasive Species Council's website: http://mdinvasives.org/iotm/sept-2017/
My apologies for taking so long to respond. I took a couple of pictures. It was very dry and hard to get a good root sample. It appears to be very shallow root. I also took some photos of the seed head.
No worries! Thank you for the additional pictures. It is definitely small carpetgrass.