The Black Hill is the volcanic cinder cone that forms the western horizon of downtown St. George. The hill rises about 500 feet directly above Bluff Street, with basalt cliff bands on the east face and a scoria-and-cinder summit. Geologically the feature is a Pleistocene-era cinder cone — one of several in the area produced by the same volcanic episode that built the Snow Canyon lava flows north of town — and the basalt cap and the lava flows that ran from it shaped much of the local geography that pioneers encountered when they arrived in 1861.
A volcano in the middle of a sandstone city
Most of St. George is built on red Navajo sandstone, the same Jurassic dune-rock that walls Zion and Snow Canyon. The Black Hill is the visible exception — a black basalt feature pushed up through the sandstone in the Pleistocene, geologically much younger than the surrounding rock. The eruption that built the cone produced lava flows that ran east and south, capping nearby ridges and creating the basalt-on-sandstone contact that locals walk past every day on the streets west of Bluff. The same volcanic episode is responsible for the lava-tube features and the petrified flow ground inside Snow Canyon State Park.
The summit walk
The City of St. George maintains the hill's summit area as informal open space. A network of walking trails climbs from the Bluff Street side and from the Sunset Boulevard / west-side residential streets to the top, gaining about 500 feet over a mile or so depending on the route. The summit holds a few small benches, the radio installations that give the hill its silhouette, and a 360-degree view: the LDS Temple and downtown to the east, the Virgin River bottoms south, Pine Valley Mountain north, and the Beaver Dam Mountains and the Mojave edge to the west and southwest. The summit is windswept, exposed, and one of the more direct urban-walks in southern Utah for the scale of view it produces.
A horizon that defines the city
For downtown St. George the Black Hill is the western horizon. The city's pioneer-era street grid was laid out to face the hill — Tabernacle Street, Main Street, and the older grid run east toward the sunrise and west toward the basalt cliff. Most photographs of the LDS Temple from the south or west include the Black Hill as the dark backdrop. The hill is the single most visible piece of geography in the downtown experience after the temple itself, and is the named feature locals point to when they orient out-of-towners to the city's compass.
What the hill is for
The summit walk is one of the most accessible walks in town — the trailheads are within minutes of the downtown core, the elevation gain is moderate, and the round trip fits in an hour or two. Locals use it for sunset, for sunrise, for short morning workouts. The basalt is an active climbing-and-bouldering substrate (the Black Rocks, on the west side of the hill, holds bouldering circuits on crystalline basalt). The 2017 fire that burned across the upper hill is still visible in the recovery patterns. It is the only volcanic cone inside the city limits of any 435 town and one of the few features in Washington County where the eruption that built it still shapes the daily commute below.