LiDAR imagery reveals the site of Mt. Gretna’s proposed Maximum Security Prison

As I mentioned in a previous article, I recently gained access to LiDAR imagery of Lancaster County. One of the first places I zoomed in on was the razed ghost town of Safe Harbor. Next, I pointed the software towards Mt. Gretna and the maximum-security prison that started construction there in 1938 but was never completed. 

LiDAR of State Game Lands 145, where the construction for a maximum-security prison started in 1938.

A Brief History

The Depression-era super max penitentiary had several unique design elements. In fact, Project architect Henry Hornbostel said that it was the first innovation in design for a prison since the then 100-year-old Eastern Penitentiary. Hornbostel insisted that this jail would be escape-proof and riot-proof.

Eastern State Penitentiary

For starters, the facility would be dominated by three massive 33-feet-tall precast concrete towers. None of them would have windows or doors. The center monolith would be a colossal 672 feet in diameter, containing 592 cells using a material designed to blunt any prison-made chisel. Good luck getting out of there, Andy Dufresne!

If a prisoner could somehow tunnel through a wall, the cells were laid out back-to-back and side-to-side, so any attempted escape would lead into another cell.

Architect’s rendering of the prison.

Prisoners would also be under 24-hour supervision. Guards would walk on top of the cells looking down through a slot in the ceiling of each.

The two remaining towers would be smaller and flank the central monolith. These 450-foot diameter silos would contain the exercise yard and dining rooms.

The entire complex would be surrounded by a “moonscape” of broken rock with no grass or trees that extended 300 feet beyond the towers in all directions. This moonscape would be encapsulated inside a 10,000 long, 12-foot high tool-resistant steel mesh fence.

This is what the prison’s “moonscape” of broken rock might have looked like.

Construction began on October 17, 1938, at the groundbreaking ceremony seen below.

The October 17, 1938, groundbreaking ceremony for the new prison.

By spring, concrete footers were being poured, manholes shaped, a sewage disposal building was walled, and an octagon-shaped foundation was poured for the water tower.

With the wheels of progress fully in motion, it appeared that nothing could stop the project. But then, newly elected governor Arthur James released his June 1939 budget. A single sentence from his budget address essentially killed the prison, “Nothing is included in the budget for opening the Maximum Security Prison at Mt. Gretna.”

Arthur H. James, Governor of Pennsylvania, 1939-1943.

Construction soon stopped, and the prison was never finished. 

Visiting the Site

I visited the site in March of 2021 with fellow adventurer Lee Winters. You can read more about that visit here. Not much was visible, though. What does is slowly being overtaken by the forest. One ruin that we located was the octagon-shaped water tower foundation. Here are several photos of the structure. You can find the octagon here.

Further up the trail on the right, you can find this row of candy cane-looking pieces of rebar. It had a slight curve, which at the time made me wonder if it was destined to be one of the three circular towers. See a photo of it immediately below.

LiDAR Imagery

With access to the LiDAR imagery, I was curious if more of the complex would be visible. I was pleasantly surprised to see that it was. The half-circle seen below was not visible when I was on site due to the ground cover and its sheer size. Remember that this tower would have had a diameter of 450 feet. That’s one and half times longer than a football field!

Next, I wondered how well the artist’s rendering of the prison would match up with the actual LiDAR. After some simple image rotation and resizing in PhotoShop, the two lined up very well. See for yourself below.

Here is the LiDAR image with an overlay of the prison.


Even more interesting is when I pulled the GPS coordinates from the photo of the candy-caned-shaped rebar, it fell exactly on the curve shown on the LiDAR map. See the following image.

LiDAR map with the candy cane shaped rebar’s location highlighted.

Planning Your Visit

You can find the remains of Mt. Gretna Maximum Security Prison in State Game Lands 145. You can access the grounds from this parking lot along Lawn Hill Road highlighted in the Google Map below.

Keep in mind that hunting is permitted on State Game Lands, and you should wear orange if you visit.

What is LiDAR?

LiDAR stands for Light Detection and Ranging. It is a remote sensing method that uses light in the form of a pulsed laser to measure variable distances to the Earth. A spinning camera attached to an airplane, helicopter, or drone emits hundreds of thousands of laser pulses per second as it flies over a specific location.

A drone carrying a LiDAR rig.

Even in areas with thick overgrowth, some of the laser beams reach the ground and bounce back. A scanner then records the returning pulses. When combined with a specialized GPS receiver and other data, complicated computer software can generate a precise, three-dimensional map sans the vegetation.

Man-made objects such as walls, foundations, and artificially leveled ground that were once hidden by plants and other greenery suddenly become visible. Archeologists have been using the technology to discover lost Mayan structures in the Amazon for several years.

Here is the LiDAR image with an overlay of the prison.


Todd Bainbridge provided these two aerial photos of the prison from May 10, 1940. They show how far construction proceeded before funds ran out.

May 10, 1940 aerial photo.

Adventure Awaits!

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