There may not be gold in them thar hills, but if you know where to look, it’s easy to find colorful and ancient rocks while walking the trails at Ruffner Mountain Nature Preserve.
Think of the mountain as a layer cake that has collapsed on one side. The steep northwest slopes of the mountain expose the oldest rocks, while the gentler southeastern slopes reveal newer examples.
The oldest is Chickamauga limestone, a bluish-gray rock found at the base of the mountain. These rocks are usually below the surface of the forest soil, but occasionally jut out from the steeper hillsides. This rock was formed as long as 488 million years ago, when much of Alabama lay beneath a shallow tropical sea. The creatures that lived in those waters – corals, sea lilies and others – left their shells behind as large limestone deposits. Look closely and you might even find some as fossils. This limestone was once quarried from Ruffner and used to help extract impurities from iron ore.
Along the crest of Red Mountain lies the Red Mountain Formation – slightly younger rocks dating as far back 443 million years. On the surface, these rocks appear just before the ridgeline on the northwest slope and reach nearly to the base of the southeast slope of the mountain. You can spot the dark purplish-red iron ore, or hematite, near the mining ruins here. Hematite was mined along Red Mountain, which takes its name from the rust-colored rocks. They even tint the soil a dark reddish-brown.
At the bottom of the southeast slopes, look for white and orange rocks near the surface and a lot of bright orange clay. These are fragments of a rock layer that formed as long as 359 million years ago called Fort Payne Chert. It’s mostly chert, which comes from the silica shells of small sea creatures. You can see the chert near the surface where the limestone has weathered away.
There’s one more rock to look for: Hartselle Sandstone, the foundation for a line of low hills that parallel Red Mountain near the base of its southeast slope. During a time when northern Alabama was covered by ocean, this sandstone was a barrier island at its edges. Now it can be found near the wetland, where a short hike up the Little Sandstone Ridge trail reveals ornately weathered sandstone with strange dimples and pock marks.
– R Scot Duncan