[1] Pilot Knob is one of around 75 late-Cretaceous Period volcanoes scattered around Central Texas from Waco to Austin, San Antonio, and Del Rio.

The complex rises above a circular lowland drained by Cottonmouth Creek and is underlain chiefly by volcanic ash and other pyroclastic debris.

A topographic rim surrounding the Cottonmouth Creek lowland to the north is formed by sedimentary rock, mainly lithified beach sediments composed of shell fragments and reworked volcanic ash that accumulated in the shallow waters around the volcano.

In late Cretaceous time, Central Texas was part of a vast marine shelf on which carbonate rocks were deposited with the entire area gradually subsiding as sediments were laid down.

The subaerial Pilot Knob ash cone allowed the intrusion of magma into the mound without contact with sea water, resulting in quieter lava eruptions.

Some of the trap rock bodies are the erosional remnants of lava flows, due to their apparent dip away from the central core area.

Exposures at other bodies of trap rock are not generally good enough to determine their exact emplacement, but some, at least, are probably plugs of solidified intrusive magma.

Magnetic anomalies on the northeast flank of the core area suggest a buried trap rock body within the ash mound, possibly a cone sheet or lava flow.

Today the terrain at Pilot Knob reflects the relative resistance to erosion of the different rock types that appear around the volcanic complex.

The volcano at Pilot Knob exerted a profound influence on the stratigraphy of the Upper Cretaceous sedimentary rocks of the Austin area.

A circuit of the volcanic complex can be made by turning right off Highway 183 onto Dee Gabriel Collins Road and heading west to the intersection with McKinney Falls Parkway.

Dee Gabriel Collins closely follows the northern topographic rim of the volcano formed by the escarpment of the Cretaceous beach rock.

[1] The second season of the American procedural drama television series 9-1-1: Lone Star featured a scenario where Pilot Knob reactivated, and the characters' attempts at saving lives as a result of the eruption.