[5] Initially described as marine shales, the 500–700 feet (150–210 m) thick Wellington appears mostly as dark gray, thinly bedded soft rock, much of it terrestrial, with sediments from fresh water ponds and salt lakes.

Marine fossils are limited to the lowest beds while the remainder features freshwater species and land life, particularly insects and reptiles.

The climate was generally arid but with cyclic variation in global temperatures and precipitation recorded by layers of windblown dust deposited in the basin.

The Wellington is not particularly rigorously divided into subunits as few easily identifiable features are consistent other than the dark shale; but certain subdivisions are recognized.

However, these informally named divisions are based only upon the position of the Hutchinson Salt Member in the general middle of the formation, which is usually but not always present.

Milan Limestone[11][12] is the marker bed for the top of the upper Wellington, but it is not always present, its absence visibly obscuring the contact with the overlying Ninnescah Shale.

[9] One outcrop is in the bank of the Chikaskia River south of Milan, Kansas, where it consists of three beds of dolomite separated by shale, all with green flecks of malachite.

[19][20][21] As a shale, the Wellington Formation has limited exposures, but tends towards forming moderate soil-covered slopes below Kiowa Sandstone caprocks.

Following Interstate 70 in Northcentral Kansas, just east of Salina, travelers are guided over a scenic range of hills between the broad Saline and Solomon valleys.

The result is lesser bluffs that are geologically similar to those formed by the Dakota Formation over Ninnescah Shale just west of Salina.

Here, flowing out of the Smoky Hills in the west, the river previously continued to the southeast, but its present course is east across the valley then turning north to Salina.

[24] Roughly 80 feet (24 m) of upper Wellington Shale are exposed from the excavation, including a color change higher on the sides and short waterfalls over resistant layers of dolomite.

Glennifer Hill Drive leads to the hilltop for parking, a panoramic city view, and trails into the diversion channel as well as to the Wellington shale exposed by the abandoned brick factory quarry now named Indian Rock Lake.

The lack of cement casing and plugging means that surface fresh water now drains down the well bores and on passing through the salt, anhydrite, and gypsum beds dissolves and carries away those minerals.

As no strong formations lie above the Hutchinson Salt (only soft shale, sand, and very thin chalk) the sinking is very steady and gradual.