These strata outcrop as isolated, lens-shaped exposures of rocks that fill erosional valleys and locally karsted topography and caves developed in the top of the Redwall Limestone.

The Surprise Canyon Formation and associated unconformities represent a significant period of geologic time between the deposition of the Redwall Limestone and the overlying Supai Group.

They referred to the strata of the Surprise Canyon Formation informally as preSupai buried valley deposits and interpreted them the sedimentary fill of paleovalleys.

[2][3] The strata, which fills the paleovalleys, karsted topography, and caves cut into in the upper surface of the Redwall Limestone, has the most varied lithology of any Paleozoic formation exposed in the Grand Canyon.

Eastward within the eastern Grand Canyon, these three units merge laterally into a single layer of red-brown, slope-forming conglomeratic sandstone and siltstone that lacks limestone.

The middle limestone unit typically forms resistant cliffs or ledges and weathers yellowish brown, rusty, or purple gray.

Where this contact is exposed, the eroded surface of the Surprise Canyon Formation is covered by (1) a thin widespread, but locally discontinuous, limestone pebble conglomerate that contains chert pebbles; or (2) purplish red calcareous siltstones and mudstones grading upward into resistant gray limestone beds containing pale red-to-orange chert nodules.

[2][3][9] The basal contact of the Surprise Canyon formation consist either of gently U-shaped or V-shaped paleovalleys scoured or paleokarst and caverns corroded into the top of the Redwall Limestone.

In other outcrops, the lower contact consists of irregular, and smaller scale pits (ancient sinkholes) and former caverns filled with reddish-brown mudstone.

[3] In addition to the plant fossils, isolated dental and dermal elements of ancient sharks have been recovered from the basal conglomerate and sandstone unit.

[1] Finally, the sandstone beds of the basal unit also contain trace fossils in the form of simple, vertical burrows and rare Conostichus sp.

[1][3] In addition, the middle limestone unit within the western Grand Canyon has yielded a remarkably diverse vertebrate fauna that consists of a total of thirty-one taxa identified from teeth and dermal elements.

The initial determinations of age relationships of the underlying Redwall Limestone, Surprise Canyon Formation, and subdivisions of the overlying Supai Group were based upon calcareous foraminifera and corals.

[1][3] The Surprise Canyon Formation is interpreted as representing the accumulation of riverine and estuarine sediments in paleovalleys and of regolith in caverns and sinkholes eroded into the exposed surface of the Redwall Limestone during the Late Mississippian.

This left the former seafloor and upper surface of the Redwall Limestone subaerially exposed as a tropical sinkhole plain drained by west-trending, low-gradient rivers.

The channels of these rivers and their tributaries eroded major drainage valleys that cut into the sinkhole plain as deep as 122 m (400 ft), 2/3 of the thickness of the Redwall Limestone.

The basal conglomerate and sandstone unit in the western and central Grand Canyon is interpreted to represent sediments deposited by these rivers during this time.

When relative sea level rose again and transgressed eastwards, the paleovalleys were gradually flooded as rivers and their floodplains were submerged to created estuaries.