Yes, I believe they have been showing this on public television about the formation of North America. I had wondered if New Madrid was somehow related to the end of the left side of the great fault.
Not sure what you mean by "end of the left side of the great fault". If, by 'left side', you mean the part of the US that was and still is west of the fault, it of course is still there, as that arm of the 3-prong fault never actually opened. It was/is a "failed" arm or failed rift. As spreading proceeded along the other two arms it stopped along the New Madrid arm. This was 600+ million years ago, during the breakup of early supercontinent Rhodinia. It was before supercontinent Pangea, which began breaking apart 'only' about 200 million years ago, eventuslly giving birth to the Atlantic Ocean. North and South America had been stuck to Africa at that time, and was South of the equator.