Recommended direction: S to N
Day hike: Yes
Overnight backpacking hike: No
Duration: 6 hr.
Early exit option: at 5.5 mi., PA 233 (limited parking)
Natural history feature: Chimney Rocks
Social history features: Remains of old ironworks charcoal staging sites; Waynesboro Reservoir; Snowy Mt. Fire Tower
Other features: Caledonia SP pool, bath houses, picnic pavilions
Shelters & camping: Tumbling Run Shelters; Hermitage Cabin; Rocky Mt. Shelters; Caledonia SP
Directions: Take I-81 N or S to PA 16 E (Exit 3), go 10.0 mi. to Rouzerville, L on Antietam Rd. (PA 2007) and 5.0 mi. to Old Forge Picnic Grounds. Parking for a dozen cars in the park lot. End: Take I-81 N or S to US 30/Chambersburg exit. Take US 30 E 11.0 mi. to Caledonia SP. Parking in lot near pool.
The Appalachian Trail follows ridges of mountains east of the Alleghenies to the Susquehanna River in a long section of Trail notorious for its foot-bruising, boot-destroying rocks. The Trail north of the Susquehanna is characterized by long, flat, rocky ridges broken by fairly strenuous climbs in and out of gaps. About ten miles south of the Susquehanna River, the Trail crosses the Great Valley of the Appalachians to the Blue Ridge. This southern portion of the Trail through Pennsylvania has many sections that are gentle, and grades are easy, making it one of the easiest sections of the Trail. Pennsylvania can be oppressively hot in summer, and water may be scarce. The Trail crosses many roads, and some shelters are near roads, where scattered crime problems make extra safety awareness a good idea. The Appalachian Trail Conservancy has a field office along the Trail in Boiling Springs. 
The hike starts with crossing the East Branch Conococheague Creek in Caledonia State Park. The park has several short trails. The Appalachian Trail also passes through part of the park, and a blue-blazed side trail is accessible. The park’s trails range from a half-mile to nearly three miles in length. The Blue Blaze Trail is seven-tenths-mile long, ascending 400 feet to Ore Bank Hill, before joining the Appalachian Trail. At just over two miles, Ramble Trail begins at the visitors’ center and passes through scenic lowlands in the park and past the Rolling Mill waterfalls. The Thaddeus Stevens Historic Trail allows hikers to inspect an old blacksmith shop, an iron furnace, Mill Race Falls and a furnace and header dam. 
After passing through the Park, the AT trail starts a nice climb up to the ridge line. 420 vertical feet over a few miles, a great way to start the hike. You can stop at Quarry Gap Shelter, a unique trail shelter in that it is overly maintained, perhaps too nice (Y2010). The shelter has a wind flap, landscaping, bench and other luxury items not normally founded in an AT shelter.
The trail through this section is some of the easier hiking found on the Appalachian Trail. The notorious Pennsylvania rocks have not yet started and the grade is fairly easy. There are even some sections that have a soft bed of pine needles covering the trail.
1.5 miles after Birch Run Shelters, the trail detours around Camp Michaux. Camp Michaux was originally part of a farm associated with the iron making operation at Pine Grove Furnace. The farm became a Civilian Conservation Corp camp in the 1930's and was finally used as a Prisoner of War camp for German POW's in World War II. Most of the buildings are gone, with the exception of a stone wall and foundation. The AT travels through many historic areas. In fact, Gettysburg is only 20 miles from this area. Many of the hills and trails to be walked over were used by troops in the Civil War. You'll soon reach Pine Grove Furnace State Park. This park is not very famous along the AT and serves as a kind of halfway point for thru-hikers (Pine Grove is located near the actual AT mid-point). 
Source: ATC, www.sectionhikingtheat.blogspot.bg
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