Defiance Quarry: Yellow Calcite & White Calcite Rockhounding in Saint Charles County, Missouri

Plan your visit

Generally open to casual rockhounding

County

Saint Charles County

State

Missouri

Nearest road

MO DD

Postcode

63341

Coordinates

38.66076, -90.77598

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Best time to visit Defiance Quarry

Comfortable months (45 to 90°F highs)

Best months: February to November. Typical highs run 88°F in midsummer and 39°F in midwinter, with winter lows near 21°F.

Climate normals: NOAA 1991-2020 monthlies, WELDON SPRING NWS station (6 mi away).

Geology at Defiance Quarry

This spot sits on ground mapped as limestone and siltstone that formed roughly 360 to 325 million years ago. Carbonate rock like this is the classic host for lead, zinc, and fluorite mineralization, which typically follows old cavities and replacement zones.

Age

360–325 Ma (Mississippian)

Rock types

limestone and siltstone

Elevation

580 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

• Missouri Geological Survey
• Mark Twain National Forest
• Missouri State Parks rules
• Community submissions reviewed against published agency rules