The Coast Guard broadcasts differential correction data on 300 kHz beacons in the US and Canada. The service is free, but only available near coastlines and major bodies of water. It does not reach to many of our hiking trails. The two nearby stations are Montauk and Sandy Hook. The low frequencies give some coverage in valleys.
Coverage is limited to areas with participating transmitters.
DCI uses WNEW xxx and covers 30-50 miles from the transmitter and is line of sight. These signals will be severely impacted by being in the radio shadow of a hill. The satellites are geo-synchronous and hence high in the sky so they should be receivable most places. Commercial base stations are expensive. See OEM GPS receivers.