There is a place called Logan. It comes under cumnock. https://en.wikipedia.org/wiki/Logan,_East_Ayrshire
It turns out that there are many places called Logan, according to the Ordnance Survey Name Books.
There is a Logan Hill in Old Deer, Aberdeenshire.
There are a Logan Bridge and Logan Hags in the parish of Auchinleck, Ayrshire.
There is a Logan Burn in the parish of Galston, Ayrshire.
There is a Logan Hill in the parish of New Cumnock, Ayrshire.
There are a Logan House and a Logan Quarry in the parish of Old Cumnock, Ayrshire.
There are a Logan Burn, High Logan, North Logan and South Logan in the parish of Sorn, Ayrshire
There is a Logan Burn in the parish of Gretna, Dumfries-shire.
There are a Logan House, Logan Mains and Logan Burn in the parish of Half Morton, Dumfries-shire.
There is a Logan Burn in the parish of Kirkpatrick Fleming, Dumfries-shire.
There is a Logan Water in the parish of Langholm, Dumfries-shire.
There is a Logan Knowe in the parish of Moffat, Dumfries-shire.
There is a Logan Gail in the parish of Wamphray, Dumfries-shire.
There is a Logan Head in the parish of Westerkirk, Dumfries-shire.
There are a West Logan and an East Logan in the parish of Buittle, Kirkcudbrightshire.
There is a Logan Farm in the parish of Balmaclellan, Kirkcudbrightshire.
There is a Logan Water in the parish of Lesmahagow, Lanarkshire.
There are a Logan House, Logan Burn, Logan Cottage and Logan Lee in the parish of Penicuik, Midlothian.
There is a Logan Burn in the parish of Glenholm, Peebles-shire.
There are a Logan Craig, Logan Head and Logan Burn in the parish of Drummelzier, Peebles-shire.
There is a Loch Logan in the parish of Gargunnock, Stirlingshire.
There is a Port Logan in the parish of Kirkmaiden, Wigtownshire.
There are a Logan House and a Logan Windmill in the parish of Kirkmaiden, Wigtownshire.
Now the really interesting thing about all these is that not one of them is in Argyll or in any other Highland county. Nevertheless, James B Johnston's
The Place Names of Scotland says that the name Logan is from Gaelic
lagan, meaning a little hollow. (As is Logie, of which there are at least as many again.)
As
pwhhh's original query specified that the Logan (s)he is looking for was in Argyll, it looks as if all these Logans can be eliminated.