Drake family history page http://www.xroyvision.com.au/drake/history/hist10.htm says Mount Drake is Musbury fort (or Castle)
Mount Drake, the original home of the Drakes, is situated in the manor of Musbury, Axminster, Devon County. Musbury is a pure Saxon name, "Maest Barrow," or "The Biggest Hill." The British name of the place was "Mae Dun," of which Maist Barrow is a translation. The old name, Mae Dun, survives in a cluster of houses about a quarter of a mile from the present village, where it is corrupted into "Mayden-hayne."
Mount Drake is a table-land or plateau of about 160 acres, half way up the great ridge which goes by the name of Musbury Castle. It was one the seat of a British, and then of a Roman, encampment, and was a fortified camp, quite capable of accommodating two hundred persons or more. It was defended on three sides by a natural ravine, and on the upper side by bogs and a tangle of brush-wood, part of which still remains.
The passage above points out that it's a pre-Saxon site yet says it's a "pure Saxon name"!