ial originating from below the earth’s crust moving up along cracks in the sandstone and solidifying into large sheets of black traprock otherwise known as dolerite. This happened approximately 170 million years ago. This traprock weathers to a brownish orange because of its iron content. Glacial activity created the final formations. Traprock resists erosion so hills were created. Streams of meltwater as the glacier receded were affected by the rise of the sea. This sent arms of rivers up beyond what is now North Haven. Sand and mud brought down by those rivers and peat formed in the salt marshes have since filled in those areas producing the flood plain through which the two rivers, the Mill and the Quinnipiac Rivers, wind their way towards New Haven Harbor and Long Island Sound. Beside the summit of East Rock are two other summits, Indian Head and Snake Rock, both formed by glacier activity. East Rock was quarried for its traprock for years. Many foundations of older New Haven homes were laid with East Rock traprock. The largest area quarried still visible is Corner Quarry, next to the Giant Steps leading to the summit.
College Woods, a level area near the Ranger Station, has gone through very few changes over the years. Many Indian artifacts found here have suggested this was the sight of a Quinnipiac village or camp sight long before the white settlers arrived in the New Haven area. Artifacts would include arrowheads, short bladed knives, and chisels. The Indians would use New Haven area rocks such as quartz, sandstone, and traprock to make these tools. They would also use rocks from other areas, west of the Hudson River, that flaked more easily such as jasper and black chert.
After years as a Quinnipiac hunting ground with the hills used as Indian lookouts, the white settlers arrived in this area. The Puritans attempted to establish a major commercial trading port. The area around the Mill River began to change rapidly. Grist Mills were built along the river and waterpowered by a low dam. In time Eli Whitney built his gun factory in 1798 on the Mill River below where the dam is today. It was here that Eli Whitney began the use of the interchangeable parts production process which became known as the American System of Manufacturing. Over the years much interest was given to making East Rock into a public park. Through generous donations of land from Yale College and individual families, East Rock Park went into operation in 1880 as a public park.
The Mill River is one of New Haven’s most beautiful rivers. It is dammed up to form Lake Whitney, a public water supply. The Lake lies in depressions created during the ice age about 10,000-15,000 years ago. The clear water coming out of the Whitney Lake supports fish and invertebrate. While the Quinnipiac tribe lived near the river, they harvested fish, crab, and shellfish from its waters. Fresh water springs ran from the base of East Rock. One hundred years ago the Mill River was a prime spot for swimming, boating, and fishing all the way down the river past Chapel Street . The park where the Mill River joins the Quinnipiac River was a popular sunbathing and swimming area. The Mill River was a tidal river healthy and abundant in wildlife.
Today the rich soil deposits of the river and its flooding and eroding action influence the plant growth in the low flood plain. There is a high water table preventing the deep penetration of root systems and secure anchorage of trees, thus many trees topple alongside the river. The black willow with its shallow, broad root system successfully thrives long the river banks. Other vegetation we find within the low flood plain of the Mill River are Pin Oak, Shrubs; such as Nannyberry and Silky Dogwood. The multiflora rose is a popular habitat and food source for nesting birds. Cattail marshes also provide cover for nesting and migrant birds. These marshes include water atruim, skunk cabbage, and swamps with woody shrubs. A very unusual fern grows in the shallow margins of the water. This unique plant is the water shamrock and looks like a 