Clackmannan, Scotland/UK Clacmanan ‘Stone of Manau’ from the Gaelic clach ‘stone’, a reference to the very old stone in the middle of the town, and Manau, the name of a district.

http://www.themodernantiquarian.com/site/812/

Off topic but does Clach a'Charra at Onich on the banks of Loch Linnhe have another name or spelling, can't find it on TMA using search.
http://www.glencoe-scotland.net/standstone.html