FLY GAP, TEXAS. Fly Gap is a half mile west of Ranch Road 1900 and twelve miles northeast of Mason in northeastern Mason County. According to legend, the community got its name from an incident involving a band of settlers who were pursuing some Indians as they retreated from a raid somewhere south of the Llano River. The settlers hid in ambush in a gap in the Kothmann Mountains and tied their horses in a nearby thicket. The outcome of the ambush is unknown, but when the men returned to their mounts, they found that the horses had been badly bitten by horseflies, and the spot was consequently named Fly Gap.