Integrative Natural History of Amnicon Falls State Park, Part 12: The Downstream View From Horton Covered Bridge | Wisconsin, USA
(Updated April 16, 2025)
Looking northwestward at the middle branch of the Amnicon River.
Horton Covered Bridge is a small but strategically placed pedestrian crossing that offers wonderful vistas of both the park's Upper Falls and Lower Falls. The latter is shown here. And around it there's a lot of North Country geology and botany to take in.
The Douglas Fault contact between the upthrust Chengwatana Volcanic Group basalt and the Bayfield Group's Orienta Sandstone is about 125 yd (115 m) behind us. So everything before us here is the Orienta. Classified as an arkosic sandstone with significant feldspar as well as quartz content, it owes its handsome brick-red to maroon color to a lot of ferric-iron oxide in the form of the mineral hematite.
As one of the ruddy-tinted clastic rocks deposited in or adjacent to the Midcontinent Rift (active ca. 1.1 Ga ago), it was marketed along with other similar formations under the generic trade name of Lake Superior Brownstone. One major quarrying locale for the Orienta specifically was the area including Port Wing and Herbster, Wisconsin, roughly 30 mi (48 km) northeast of the park. Stone produced there was used in architectural projects in such cities as Peoria, Illinois; Fargo, North Dakota; and Lincoln, Nebraska. But my own favorite example is the Historic Old Central High School in nearby Duluth, Minnesota.
On both sides of the Lower Falls the Orienta Sandstone is very flaggy, thin-bedded, and almost flat-lying, in contrast to the contorted and tilted strata found closer to the fault. However, its most dramatic exposure is the high cliff carved by the river where it makes its turn to the left. The flat surfaces of this vertical face are the result of sheet spalling due to rock splitting along high-angle joints.
The rich earth tones of the bedrock are complemented by the greens of the forest that thrives atop it. Three tree species dominate the scene. The most lordly of these, Eastern White Pine (Pinus strobus), is the tallest. It can also be identified by its feathery foliage (five slender needles per fascicle) and its open crowns with horizontally spreading branches that tend to curl up just a little at their tips.
The other pine present is the Red (P. resinosa). Its stouter needles are bound two per fascicle and tend to form clumps or clusters on their stems. Red Pine is renowned especially for its straight boles, which have made it a primary choice for foundation pilings (such as the kind many of Milwaukee's older tall buildings rest on) and telephone poles. There are some good examples of this species on the frame's left margin.
A little less obvious here is the one really abundant broadleaf. Its strikingly white trunks can be spotted on either side of the great Eastern White Pine at upper center. It's the Paper (or Canoe) Birch, Betula papyrifera.
In this photo, multicellular animal life seems to be restricted to two bipedal primates belonging to Homo sapiens subsp. turisticus f. bermudashortsensis. Special care must be taken when encountering this creature in parkland settings. Or anywhere else, for that matter.
You'll find the other photos and descriptions of this series in my Integrative Natural History of Amnicon Falls State Park album.
Integrative Natural History of Amnicon Falls State Park, Part 12: The Downstream View From Horton Covered Bridge | Wisconsin, USA
(Updated April 16, 2025)
Looking northwestward at the middle branch of the Amnicon River.
Horton Covered Bridge is a small but strategically placed pedestrian crossing that offers wonderful vistas of both the park's Upper Falls and Lower Falls. The latter is shown here. And around it there's a lot of North Country geology and botany to take in.
The Douglas Fault contact between the upthrust Chengwatana Volcanic Group basalt and the Bayfield Group's Orienta Sandstone is about 125 yd (115 m) behind us. So everything before us here is the Orienta. Classified as an arkosic sandstone with significant feldspar as well as quartz content, it owes its handsome brick-red to maroon color to a lot of ferric-iron oxide in the form of the mineral hematite.
As one of the ruddy-tinted clastic rocks deposited in or adjacent to the Midcontinent Rift (active ca. 1.1 Ga ago), it was marketed along with other similar formations under the generic trade name of Lake Superior Brownstone. One major quarrying locale for the Orienta specifically was the area including Port Wing and Herbster, Wisconsin, roughly 30 mi (48 km) northeast of the park. Stone produced there was used in architectural projects in such cities as Peoria, Illinois; Fargo, North Dakota; and Lincoln, Nebraska. But my own favorite example is the Historic Old Central High School in nearby Duluth, Minnesota.
On both sides of the Lower Falls the Orienta Sandstone is very flaggy, thin-bedded, and almost flat-lying, in contrast to the contorted and tilted strata found closer to the fault. However, its most dramatic exposure is the high cliff carved by the river where it makes its turn to the left. The flat surfaces of this vertical face are the result of sheet spalling due to rock splitting along high-angle joints.
The rich earth tones of the bedrock are complemented by the greens of the forest that thrives atop it. Three tree species dominate the scene. The most lordly of these, Eastern White Pine (Pinus strobus), is the tallest. It can also be identified by its feathery foliage (five slender needles per fascicle) and its open crowns with horizontally spreading branches that tend to curl up just a little at their tips.
The other pine present is the Red (P. resinosa). Its stouter needles are bound two per fascicle and tend to form clumps or clusters on their stems. Red Pine is renowned especially for its straight boles, which have made it a primary choice for foundation pilings (such as the kind many of Milwaukee's older tall buildings rest on) and telephone poles. There are some good examples of this species on the frame's left margin.
A little less obvious here is the one really abundant broadleaf. Its strikingly white trunks can be spotted on either side of the great Eastern White Pine at upper center. It's the Paper (or Canoe) Birch, Betula papyrifera.
In this photo, multicellular animal life seems to be restricted to two bipedal primates belonging to Homo sapiens subsp. turisticus f. bermudashortsensis. Special care must be taken when encountering this creature in parkland settings. Or anywhere else, for that matter.
You'll find the other photos and descriptions of this series in my Integrative Natural History of Amnicon Falls State Park album.