Why is Peavine Island in York County?

When York County was formed from Lancaster County in 1749, Lancaster County kept all of the Susquehanna River, therefore the boundary line was established on the York side of the river. Then why are four Susquehanna River islands located in York County?
Today we’ll look at Peavine Island in Lower Chanceford Township. Peavine Island is located just downriver from Holtwood Dam and the Norman Wood Bridge. Every map that I’ve seen shows this island in York County. This is one of those islands that fluctuate between an island and a peninsula depending on the water level in the river.
My guess at the explanation of why the island is in York County goes as follows. The boundary line was established when the river was at low level, resulting in a peninsula and therefore it was placed in York County.
From aerial photos, historical maps and various online services, about 50% of the time Peavine appears as an actual island. This is likely why the locals called it an island. Does anyone know why it was named Peavine? This island is loaded with many unique geological features.

Pennsylvania Geological Survey’s (PaGS) Photo Gallery contains a picture of the Holtwood Pothole feature on Peavine Island. It is described as, “in the Octoraro Formation in the Holtwood Gorge along the lower Susquehanna River, York County. The pothole is 4 to 7 feet in diameter and at least 28-feet deep; the bottom is buried in water and sediment.” Note the size of the pothole in relationship to the size of the person in the lower part of the photo.
Many years ago while I was walking the Mason-Dixon Trail from the Lock 12 Site southward I walked the paths leading unto Peavine Island. The island’s varieties of rock formations were impressive.
Here is a link to a web site that documents a more recent walk in the same general area. Check out the exceptional photography on this site, the area’s natural beauty is just as impressive as I remembered!
An Internet search reveals that The Holtwood Pothole and several other features on Peavine Island are favorites of rock-climbers. Several web sites are devoted to rock-climbing on this island; one of the better guides is at PaClimbing. All warn that if the siren sounds at the nearby Holtwood Dam; this means they are releasing water. The water rises quickly, meaning that you may not be able to leave the island if you do not act quickly to leave.
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