The Jackson Purchase triple junction

Steven’s question:

“Where is the Purchase area’s ‘continental divide’? Marshall, Calloway, and some of McCracken all have creeks that flow east towards the Tennessee River. Fulton, Hickman, Carlisle, and Ballard flow east or north to the Mississippi or Ohio. I think most of Graves flows west into Mayfield Creek, but some goes into Clark’s River, right? Somewhere, there’s a hill that splits the three and that’s really interesting to me.”— Steven P.

You looked at maps and called Wice Church Rd, between St. John’s and Boaz, as the line. Same county, same community, ~2 km south on the next church-named road over:

Coordinates: 36.9665° N, 88.6795° W
County: McCracken County, KY
Elevation: 492.6 ft
On the road: St John Church Rd — the triple-point sits 9 m from the centerline, and the road peaks at 494 ft right at the divide.

You were reading the landscape — the divide really is right there in St John’s, named after the same community you flagged. The three-ocean ridge is a 494-ft saddle on a back road, exactly the kind of detail most online maps round off. Good instinct.

Map of the Jackson Purchase showing the three watersheds across all 8 counties, with the triple junction marked in McCracken County. — Tan drains to the Mississippi. Blue rides the Tennessee into the Ohio. Green goes to the Ohio direct. Yellow star is the triple junction; coral dot is the Wice Church Rd call.

And the saddle itself, with rain you can actually move around:

Aerial view of the triple junction area in McCracken County. — The saddle, ~1.5 km across. Each line is a raindrop’s actual path: green ends up in the Ohio, blue rides the Tennessee, and tan goes Mississippi-direct. Yellow ring is the triple-point. Hit **Gravity Mode** (top right) and then tap anywhere to make it rain there.

Drainage streamlines color-coded by destination watershed. — The saddle, ~1.5 km across. Each line is a raindrop’s actual path: green ends up in the Ohio, blue rides the Tennessee, and tan goes Mississippi-direct. Yellow ring is the triple-point. Hit **Gravity Mode** (top right) and then tap anywhere to make it rain there.

This kind of point — three drainages, gradient zero, three valleys and three ridges alternating — has a name in geometry: a monkey saddle. There are three others in the contiguous United States. Catalog of all four →

If this kind of thinking is useful for the work you’re doing, let me know →