Joe got it. We were at Rocks State Park (formerly Deer Creek State Park) just north of Bel Air in Harford County. In Booth's letters to [Thomas] William O'Laughlen he mentions this area twice.
August 8th, 1854:
"I paid another visit to the Rocks of Deer Creek the other day. it looks just the same and sunday I whent to that large camp meeting with the hope of seeing you there. but I was dissipointed. I saw John Emlet there or that fellow that works in your shop. The Indian's where up here the other day with their great Bear."
June 18, 1855:
"Then comes the grand affair. A pick nick party to be held on the rocks of Deer crick. Thirty-seven couples to attend"
Asia writes of these rocks as well in reference to John:
"John is going on a picnic to the rocks tomorrow. Oh, those great rocks." - Letter from Asia Booth to Jean Anderson, June 28, 1855.