Las Vegas Wash — Amethyst

A historical occurrence, not a verified pin

The locality begins with a short 1953 Rocks & Minerals occurrence notice describing massive amethyst in a dark-brown porphyritic rock from Las Vegas Wash, Clark County. The notice names a broad drainage, not a surveyed outcrop. No primary source recovered so far ties the report to the precise coordinate shown on modern maps, and repeated web coordinates are not independent confirmation.

The unresolved evidence is the original page context, contributor or collector identity, specimen label, and the bibliography behind the Las Vegas Wash entry in Minerals of Nevada.

What a site visit actually found

This page is one of the few in the atlas whose coordinate comes from standing on it. A 2026 visit to the wash trail downstream of Lake Las Vegas found quartz and no amethyst — massive white to vein quartz, some carrying a peelable black mica layer, most likely biotite, turned up in a small incised ditch. The map pin now marks that trail rather than the much broader drainage the older listings pointed at, roughly fifteen kilometres upstream.

Read that as the current state of the evidence, not as a verdict. One visit failing to reproduce a seventy-year-old report does not disprove it; the wash is long, and the 1953 notice never said where along it. But anyone arriving expecting purple crystals because a dozen sites repeat the word “amethyst” should know that the person who went looking came back with quartz.

The page keeps the amethyst name because that is what people search for. It would be easy to quietly drop the term and harder to be useful.

Why the lower wash remains geologically plausible

The geology north of the River Mountains gives the historical description a credible regional setting. USGS Bulletin 936-L describes reddish-brown latite with plagioclase and biotite phenocrysts, chocolate-colored stony volcanic glass, biotite-bearing vitrophyre, and mostly porphyritic latitic lava and flow breccia in the Three Kids district. It also describes a basal conglomerate containing volcanic pebbles, cobbles, and boulders in a reddish-brown matrix, plus unconsolidated gravel locally tens of feet thick.

That creates two plausible, still unproven pathways. Amethyst-bearing material could have weathered directly from a porphyritic volcanic unit, or an older volcanic clast could have been incorporated into conglomerate and later released into younger terrace or wash gravel. Either model fits a loose specimen reported only as coming from Las Vegas Wash better than an assumed modern stream-bank vein.

NBMG Map 67 is the detailed bedrock map for the Henderson quadrangle. Map 193 separates modern Las Vegas Wash alluvium from older fan, terrace, and ephemeral-wash deposits. Those older gravel surfaces and natural gully cuts are the more useful places to inspect for provenance; engineered channel rock, road base, landscaping stone, and mine fill can produce misleading float.

What to look for

Prioritize natural cuts through older gravel or conglomerate, especially where resistant cobbles weather from a distinct layer. Useful observations include repeated white-to-purple quartz fragments, dark-brown porphyritic matrix, feldspar or biotite phenocrysts, chalcedony or opal coatings, and whether pieces are angular, rounded, embedded, or loose at the base of a cut.

A repeated cluster emerging from one bed is stronger evidence than a single surface specimen. Photograph material in place, record the layer and landform, and verify ownership, claims, and collecting rules before removing anything.

Three Kids is not a field-collecting target

Three Kids was an open-pit manganese mine, not an asbestos mine. Nevada environmental records document lead-, arsenic-, manganese-, and petroleum-affected mine materials; an asbestos survey addressed site debris and structures. Cleanup began in 2024 and remains ongoing. Do not enter pits, tailings, waste areas, fenced property, or active remediation and construction zones.

The former mine is useful as a geological reference because its USGS report documents the nearby volcanic, conglomeratic, gypsiferous, tuffaceous, manganese, opal, and zeolite-bearing sequence. It is not an appropriate casual rockhounding destination.