Peters Mountain is a peak (1190 feet) of the Appalachian Mountains on the east side of the Susquehanna River in northern Dauphin County, PA.

The place was named for Peter Allen, a pioneer settler of the area.

Peters Mountain is near the town of Halifax, PA and across the Susquehanna River (and slightly downstream) from Duncannon, PA.

https://en.wikipedia.org/wiki/Peters_Mountain_(Pennsylvania)

There is a scenic lookout on the Appalachian Trail near the top of the mountain, and this postcard photograph appears to have been taken from that spot.

https://www.visithersheyharrisburg.org/trails/adventure-trail/hiking/peters-mountain-ridge/

This postcard was originally published by J. B. Hoffman of Harrisburg, PA, but was re-published by the huge postcard firm of Curt Teich & Company of Chicago.

https://en.wikipedia.org/wiki/Curt_Teich

I cannot determine a date at which the postcard may have been first published, but the “colortone” re-publication was circa 1940.

On clear days, from Peters Mountain one can see the city of Harrisburg and discern the ridges of valleys of Juniata County across the Susquehanna.

https://en.wikipedia.org/wiki/Juniata_County,_Pennsylvania