Old Deadwood VS New Deadwood
Old Deadwood is about a 30-minute walk+Boat north. I remember setting out on foot till we came to a river-head (ie, dead-end). We made boats and continued down the river to the New Deadwood location, which has two rivers. One on the west, one on the east, both about a minute walk apart, not very large.
Here are some old pics I found of Old Deadwood, to the north-north-west.

Here is the ore smelter, seen from the Ore Smelter Wiki page, of the Mine across the river from New Deadwood.

New Deadwood's town center:

Edit;
Found an old map file of Old Deadwood, found the grid for it! 94,-79. Now, we headed south-east-south from there to find our new location...
Edit 2;
124, -68 is my best bet of the closest location. The long river going westward is likely the river that we built the boats to go down, and I vaguely remember entering a lake and going to the other side of it. I vividly remember that shiny spot in it and the lake layout. Yes, the memory of that place is returning to me.
We headed down the far side of it and south-eastwards, then south... Looks like I'm going on quite the expedition tomorrow.
I actually found a couple of hearth secrets, too, that may be active, i'll try those first.