Look for the links about county formation in the first two paragraphs, above the table of counties. They include a link to a downloadable PDF of maps during different periods. Look for the hyperlink "this excerpt overview."
The map I consult the most about Old Guilford, which shows the old line between Old Rowan and Old Orange, is not online. But roughly the western 2/3 of Old Guilford came from Old Rowan, and the eastern 1/3 came from Old Orange. Randolph was created out of the bottom 1/3 of Old Guilford in 1779, and Rockingham was created out of the top 1/3 in 1785.