Bob,

In the days before the use of trinomials, a quadrangle system was employed in Texas, used primarily during the River Basin Survey times. That system used a number followed by a letter followed by a number; the individual site number within that area followed a dash.The system was also used by some avocationals,
such as King Harris in Dallas. I think he continued using quadrangle designations after the state switched to trinomials.

Area 39D4 is located in Bell and Coryell counties, maybe some slop over into McLennan. This is the Lake Belton area, though Hillsboro is closer to the Lake Whitney work. I didn't find a 39D4-3A; 39D4-3 is 41BL63; 39D4-33 is 41CV37. On a quick glance, I didn't see any evidence of a collection from the former;
the inventory from the latter ended at 43.

So, we can provide a general explanation of the number, but at this point, can't determine a specific site or swear that it truly belonged to the Lake Belton work. A cataloged artifact showing up in road gravel boggles the mind.

Carolyn