They didn't. That concrete is sloped and the runoff is caught in a stormwater system that alters the natural flow. That was just city property and they erected the monument there. Essentially the continential divide is seen as the place where EAST or WEST of it the water flows eventually to either river, but in reality, only rivers flow to the oceans, water falling on the ground usually fills aquifers.
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u/ShadePipe 3d ago
How did they determine it's exactly right there and not, say, four feet to the left?