The sediments that underly the Isthmus of Manchac were deposited by a northward distributary of the meandering Mississippi River delta as it migrated eastward, just off the Gulf shore about 4,000 years ago as it built the St Bernard Delta. Two lakes – Maurepas and Pontchartrain – slowly appeared as the fresh alluvium deposited on either side of this feature slowly compacted.

2,200 years of Indian occupation on this isthmus had left no signs, until the I-55 Borrow Canal was dredged up in 1975 and Native American artifacts were found in the banks of Bayou Jasmin (now popularly called Shell Bank Bayou) on the narrowest part of the isthmus near Ruddock. Study by LSU Archaeologist revealed how far-ranging the Indian’s trade networks were from this seemingly isolated spot as they found stone artifacts from the Midwest. (See https://www.crt.state.la.us/dataprojects/archaeology/bayoujasmine/assets/bayou-jasmine2.pdf and https://www.crt.state.la.us/dataprojects/archaeology/bayoujasmine/)

Significant European history happened where the Greenway crosses Pass Manchac. The French first passed through here in their first explorations in 1699 and later colonist used the Pass to reach the streams that led to their many settlements in the area. The channel eventually became an international boundary between French, Spanish, English and American claims. Ambitious American entrepreneurs spanned the isthmus for the first time when the New Orleans, Jackson & Great Northern railroad was built in 1854. The entrance to the Pass was fortified and patrolled when the railroad’s bridge was burned shortly afterward in the Civil War.

After the automobile became popular, the first highway, the New Orleans-Hammond LA 33, was built in 1923 by digging a canal to build a roadbed. In 1961, the more modern highway US 51, now officially the Manchac Greenway, was built to replace it and both of these roads were replaced in 1978 when the elevated Interstate-55 was built in a canal dug alongside. LA 33 was abandoned and US 51 was officially designated as a “Frontage Road” and immediately saw much less traffic.

With the help of the railroad, the original cypress forest on the isthmus underwent wholesale industrial logging in the 1880s-1920s. Unfortunately, it could not regrow or flourish as it once had because man-made Mississippi River levees built in the 1930s cut off nourishing spring overflows and Manchac’s two tidal passes brought in an increased amount of saltwater from the ill-conceived, and now closed, Mississippi River Gulf Outlet. This has helped to convert much of the isthmus into intermediate marsh.

The ditches and elevated ground in the transportation corridor on the isthmus have made it’s immediate footprint radically different from the surrounding swamp and marsh. Because of its aereated soils it has plant life that doesn’t normally grow in the wet, stringent conditions of the surrounding innudated wetlands. Ironically, these include Hackberry, Elm, Oak, Swamp Maple and Black Willow trees – much the same species that also grow on old, meandering natural Mississippi River levees and shoreline Cheniers (beach ridges) across south Louisiana’s coastal plain. The blanket of this robust, rooted vegetation and the new rock armoring on the lakeshore make the isthmus a “Coastal Line of Defense” in Louisiana’s scheme to protect its erroding coast.

This twenty-three mile long transportation corridor through the wetlands between Laplace and Ponchatoula joins two of Louisiana’s great historic and cultural regions – the River Parishes to the south and the Florida Parishes to the north. It is largely empty of habitation except for the villages of Frenier near Laplace and Galva and Akers on either side of Pass Manchac. After having had such useful and busy past, the “low road’s” many convenient access points to surrounding wetlands and waterways, scenic beauty, wildlife and history remain. Indeed, it already functions as a greenway by providing the public acrss to many and varied recreational opportunities.