Geology of the Highland Park Neighborhood
Article by Bill Chaisson
The Highland Park Neighborhood is located between I-490 to the north and the Pinnacle Range, which forms the southern boundary of the city between the junction of I-590 and I-490. I-490 was built on top of the old commuter-rail line that led out to Pittsford. Those tracks had been laid on the old path of the Erie Canal, which came in from Pittsford to the east and crossed the Genesee River on what is now Broad Street in downtown Rochester. The canal was moved to its present location (cutting through Genesee Valley Park) early in the 20th century.
The Erie Canal was built in its original location because there is a natural east-west lowland between the Niagara Escarpment to the north and the Onondaga Escarpment to the south. Downtown Rochester is built on the Niagara Escarpment and Buffalo and Syracuse are built on the Onondaga Escarpment. The rocks of the Niagara escarpment would not be a particularly visible in this region except that in the last ~10,000 years the Genesee River has cut down into the local bedrock to form the Rochester Gorge. The top of the escarpment is made up of the dolomite rock of the Lockport Group; these rocks are visible in the bed of the river between the Court Street Dam and the High Falls. (For more information about Rochester geology, look here .)
The dolomites (similar to limestone, but rich in magnesium) of the Lockport Group are buried deep beneath the Highland Park Neighborhood under many meters of glacial moraine. The dolomites were formed in a shallow tropical sea 420 million years ago. At that time the proto-North American continent was located in the subtropics of the southern hemisphere (~25°S). The Rochester area may have looked something like the modern Bahamas, but the carbonate platform was located in the continental interior. The glacial moraine (unstratified sediment derived directly from the ice sheet) was deposited during the last advance and retreat of continental ice sheets between 120,000 and 10,000 years ago.
There is no bedrock outcrop in the Highland Park Neighborhood, but excavations in the area often unearth large boulders of Lockport dolomite. These were dislodged from the bedrock by the ice sheets of the Pleistocene Epoch (last 1.7 million years of Earth history). They are sometimes deposited by the ice many miles from their point of origin. For this reason they are called ‘glacial erratics’. But most erratics are actually deposited a few hundred yards after they are picked up by the ice, as is the case for the Lockport blocks derived from the Niagara Escarpment and found in the Highland Park Neighborhood.
Building the Landform: Some early ideas
|The first description of the Pinnacle Range in the geological literature was made by James Hall. He made a sketch of the cutting created by construction on Monroe Avenue.|
|Charles Dryer referred to the range as a “gigantic kame” and noted that “the lower half is composed of coarse gravel and the upper half of sand. A kame is composed of stratified sediment deposited by glacial meltwater into either a periglacial lake (“kame delta”) or into a supraglacial lake.
|Warren Upham referred to the range as an esker. This was completely incorrect. Eskers are composed of stratified sediments deposited in sub-glacial streams.
|Herman LeRoy Fairchild, professor of geology at the University of Rochester, accurately described the formation of the range in Proceedings of the Rochester Academy of Science, 6:141-194.
Only at Pinnacle Hill is the range a single ridge. Elsewhere it is broken up by kettles. Kettles are depressions that form when large blocks of glacial ice are left buried in proglacial sediment after the main body of the ice sheet melts back. After the ice melts, a depression remains on the landscape. “Kettle and kame terrain” is indicative of an episode of rapid ice-sheet recession. In addition to the natural depressions created by the kettles, there are numerous depressions that are the remains of old gravel quarries. Quarrying created the valley behind Lamberton Conservatory in Highland Park.
The north slopes of the Pinnacle Range were originally irregular, studded with spurs and ravines, partly erosional and partly caused by ice-contact. The south slopes were less steep with the lower portions fairly uniform; they were formed by outwash. The sediments that make up the bulk of these hills were deposited into a periglacial lake called Lake Dana ~11,000 years ago. Hence their bases are composed of more or less horizontal beds of sand and gravel.
The Pinnacle Range As a Natural Resource
Dumble rode to end of the street-car line, disembarked and crossed the canal. This former street-car stop is presently the site of the Monroe Avenue overpass on I-490. He then cut through Crosman’s nurseries (now the Laburnam Crescent vicinity) on the way to “the bare grassy hill immediately to the east of the Pinnacle cemetery”. It was an Irish Catholic cemetery located at the junction of Clinton Avenue and Field Street, which at the time was called “Paddy Lane”.
The southern edge of the city is described as being “at a distance of a long rifle shot”and the intervening fields are full of “great boulders of conglomerate limestone and granite”.
Between the time of Nathaniel Rochester’s original 1811 survey of the 100 Acre Tract for residential lots and Dumble’s walk —75 years— the Pinnacle Hill vicinity had been:
- cleared of timber —only scattered ancient oaks remained
- perhaps grazed —no fences are described, but the land is presumably kept open somehow
- quarried for gravel —Dumble does not describe a use for the gravel, but it was frequently used as fill for road construction and for making concrete.
- in use as a Catholic cemetery, including the grave of Civil War hero Patrick O’Rorke. Most of these graves, including Colonel O’Rorke’s, were moved to Holy Sepulchre Cemetery in the 1930s, but some remain, mistakenly left behind.
Note: this article was written in 2002 by former resident and one-time University of Rochester geology professor Bill Chaisson. it was written before the neighborhood officially changed its name from “Ellwanger & Barry” to “Highland Park”