I am sorry to say that I can see no evidence of Kimberlite or Diamonds but due to the area that you are in and the type of Quartz you are finding, there may be Gold on your' property! However, the bigger concern is that I believe you have a ticking time bomb on your' hands. What you described is an area that is pooling water during rain events in a bubble-like way underneath the surface thus the inflated appearance (swelling) which is likely the case. During heavier rain events, it is able to relieve some of the pressure via all the holes that are popping up (appearing) as you described and the stepped appearance is likely collapse of the underlying rock and soil. The trees are likely dying due to the water that is retained in the bubble is stagnating, becoming toxic to plant life and killing the trees from the inside out. The trees that are dying were likely the only thing keeping a geological/hydrological disaster from occurring on your' property. Another possibility of the trees dying, is that raw sewage or toxic chemicals are flowing into or leaching onto your' property which could also explain the swelling of the surface due to gases trapped below the surface. You likely have several scenarios which could or may occur. 1) The ground could swell during a heavy rain event and when it can hold no more, there could be a total blowout which could cause flash flooding, risking not only the remaining trees but also risking life and property. 2) Repeated pooling of water which when it is not getting relieved on the surface, will eventually find another avenue to relieve the pressure through the rocks and surface below and could open up a large sink hole or an opening to a large cave system.
I would advise contacting the USGS (United States Geological Survey) and Forestry Service or a Geologist and Botanist from a local University and have them come out an assess the situation on your' property. You also might ask the Hydrologist from the National Weather Service Forecast Office in Atlanta to come out and see what he or she thinks of the situation as well.
Frank