Probably this picture is from 1890-1893. There’s the same stone “seat” in this picture as is seen here.
The Park Board took ownership of the Falls in March of 1889, and all the lawsuits against this condemnation got settled within a year or two or three. They built their stone platform in 1889, and it seems they continually had to rework and rebuild it over the years.
Though some other, later pictures taken from this approximate location show a solid surface, here’s is a rivulet of water across a dirt surface and a lot of muddy footprints. Probably this is from recent rain (just look at the Falls, above), but it could be groundwater management issues.