It is thought St Helen's Loch was man made to create water for the industry that once flourished in High Bonnybridge, on the south bank of the canal. Indeed, at the "Radical Pend" there is a plaque stating that the water flowing out of a tunnel and through the Pend has originated at the loch.
Looking at maps there is a very angular flow of water between Bonnyside Road and Harley Gardens which seems to mysteriously start and end in the middle of nowhere! I have yet to fully explore this and certainly the end at Harley Gardens is likely to run underground towards the Pend. This is exactly the area where many heavy industry plants were situated.
On the north shore of the loch is an small hill. I assumed this was man made when the loch was dug out. From a bit of research and an article from Greenhill Historical Society this is Elf Hill, a mound of moraine which was laid down by a glacier during the ice age.
From the Loch it is a short walk through the Gorse field to Rough Castle, a Roman Fort which was built on the Antonine Wall. There is sometimes cattle in this field, although it is a right of way, so keep Geomutts under control.
The cache is a small tub.
Congrats to Scotbrain for FTF!