💎 Missouri’s Rosy Heart: The Granite Shut-In EC EarthCache

💎 Missouri’s Rosy Heart: The Granite Shut-In

Hidden in Madison County lies a spot where Missouri’s oldest rocks still blush pink. The Castor River Shut-Ins Natural Area is the state’s only known pink granite shut-in, sculpted over ~1.5 billion years of water versus rock. Come meet the cast: ancient granite, a determined river, and you—today’s geologic detective.

🧭 Educational Objective

• Understand what granite is and how it forms
• See how “shut-ins” develop where streams cross erosion-resistant bedrock
• Identify minerals that give the rock its pink hue
• Connect bedrock geology to the surrounding cedar glade ecosystem

Learn more via:
Missouri DNR – Geology Division • Missouri Natural Areas Program • Cedar Glade Trail (AllTrails)

📍 Trail & Access Information

Hours: Sunrise to sunset (day-use only)
Fees: None — free parking and entry
Trail: Cedar Glade Trail — ~1-mile loop to the shut-ins (natural surface with bedrock)
Nearest Town: Fredericktown, Missouri

📚 Background: How Missouri’s Rosy Heart Came to Be

Welcome to the St. Francois Mountains—one of the rare Midwest regions where Precambrian rocks stand exposed. Roughly 1.5 billion years ago, magma cooled slowly deep underground to form Breadtray Granite, a coarse crystalline rock rich in pink potassium feldspar, clear/gray quartz, and black mica. Think of it as a patient masterpiece—formed grain by grain beneath an ancient volcano field.

Erosion over countless eons peeled away younger layers until the granite emerged at the surface. The Castor River now slices through this tough bedrock, creating a narrow “shut-in.” During floods, sand and pebbles swirl like nature’s polishers, carving potholes and smoothing grooves. Feldspar’s iron content gives the rock its famous pink hue, while weathering turns it gray on drier surfaces.

Even the vegetation owes its personality to the stone. Thin, sun-baked soils above the granite form igneous glades—open, rocky clearings dotted with shortleaf pine, little bluestem, and cactus. It’s a place where geology writes poetry in both rock and root.

📸 A Look at the Stone Itself

Pink granite similar to that found at the Castor River Shut-Ins. The pink hue comes from potassium feldspar crystals.

🧭 Logging Tasks

Answer the following based on your on-site observations (and one from the background info). Send responses via the Message Center or email.

1. Granite’s Grip – Mineral Weathering Up Close
   ➡️ Examine the granite surface. Which mineral color (light gray quartz, pink feldspar, or black mica) seems most resistant to erosion—and why?


2. The Water’s Signature – Reading Flow Energy
   ➡️ Find a groove or pothole in the bedrock. Does its shape suggest powerful floods or steady, gentle flow? What clues support your call?


3. The Pink-to-Gray Mystery – Chemical Weathering
   ➡️ Compare dry rock above the waterline to rock near the stream. How do the colors differ, and what process might cause the change?


4. Missouri’s Ancient Story – Background Connection
   ➡️ According to the background information above, roughly how old is the granite exposed at this site, and what type of rock is it classified as?


5. Optional Life on the Rocks – Geology Shapes Ecology
   ➡️ The "Granite Glades" sign describes how plants and animals adapt to this rocky environment. What environmental conditions make these glades unique, and how does the Missouri Department of Conversation maintain them?


6. Optional "Pink Rocks"
   ➡️ According to the information at the "Pink Rocks" sign, what geological process formed the pink granite seen at the shut-ins, and what material gives it its pink color?


7. Optional Photo Task (No Faces Required)
   📸 Optional – Share a photo of the shut-in bedrock highlighting one feature you described (groove, pothole, mineral contrast, or glade view). Include a small personal item for scale (hat, GPS, or pen). People are not required in the photo.

🪧 Site Guidelines

• Stay on designated trails and bedrock surfaces—granite can be slick when wet.
• No rock collecting or hammering (protected natural area).
• Pack out what you pack in; respect plants and wildlife.

Permission for this educational EarthCache granted by the Missouri Department of Conservation.

Enjoy your visit to Missouri’s Rosy Heart—where water, stone, and time tell the state’s oldest story…and you get to read the next chapter.