author: Pat Reilly
date: March 2005
To talk about Gettysburg’s Rock Creek, we must talk about diabase. I first read about diabase in Ed Gertler’s Keystone Canoeing guidebook. When boating Marsh Creek, Rock Creek’s sister creek, I learned to identify the rounded boulders characteristic of this hard igneous rock that forms the creek’s rapids. Diabase was first mentioned in this newsletter during the very first ROM - Conewago west. In this bigger York County creek the diabase belt (as Gertler refers to it) shows itself in the usual fashion. You’re paddling along on a typical central Pennsylvania flatwater creek, when suddenly big round rocks litter the creek bed making for an interesting challenge as you slalom through them. Conewago has little gradient when crossing the diabase, so it doesn’t form any real rapids, but you will definitely notice when you cross the belt, it is very distinctive. Besides Marsh and Conewago west there are 2 additional creeks on either side of Rock Creek that have diabase formed rapids – Middle Creek in Adams County and Bermudian, a tributary of Conewago.
So I couldn’t help but wonder what the heck was going on with Rock Creek. Gertler rates it as a class 1 and makes no mention of diabase or rapids. For this reason (and because of a scenery rating of only ‘fair’) I passed this creek up for many years. Then on Christmas Eve of '04, I pulled up to the route 97 bridge over Rock Creek just south of Gettysburg to finally paddle it. It only took one glance, before I even got out of the car, to see where the diabase was. About 100 yards upstream from the bridge, I could see black boulders and white water (diabase is sometimes called black granite). Gertler must have missed it since his write-up of Rock Creek begins at this bridge. I can only speculate that it must have been summer when he ran this creek as brush and foliage would have prevented him from seeing the rapids. I’m sure he would have been as enticed by the diabase as I was.
Since I had the wrong boat for rapids that day, after my run down the lower creek, I scouted the diabase section in anticipation of the next trip. After looking at the rapids, I had diabase on the brain. Returning home I got on the web, printed off a geologic map of Pa and began to take an overall look at our state’s diabase. The so-called belt arcs through the piedmont parallel to but below the last mountains of the ridge and valley region. Its line is rough, not continuous, but blotchy with a thin strip here and a patch there. It is rather sparse, but as I transposed it over topographic maps, I could see that where water contacts diabase, you can almost count on rapids. In fact, it appears that at least half of the rapids in Pennsylvania’s piedmont region are the result of diabase.
Besides Middle, Marsh, Rock, Bermudian and Conewago, the rock is responsible for the ultra tight slot rapids of Beaver Creek draining Pinchot Lake and the two gnarly sections of Conewago east on the other side of the river. It is diabase that fills the Susquehanna’s river bed at Falmouth, forming Harrisburg’s best big water play spot. Further east diabase is present in Montgomery County’s surprising whitewater run – Unami Creek. It forms rapids in the upper (above Lake Nockamixon) section of Tohickon Creek. And it serves up the biggest rapid on the Delaware at the wing dam at New Hope. Off the water, the mountain at Ski Roundtop consists of diabase as does Dauphin County’s Roundtop, a large hill southwest of Hershey where the Schreiners had their kayak businesses. Yep, there may not be a lot of it, but this rock sure makes a name for itself in Pennsylvania.
I got the chance to go back to Rock Creek in mid January and returned with two fellow creekers. We put on at the next bridge up, route 116 east of Gettysburg. The trip to the 97 bridge is 2 miles and it is all bordered by the Gettysburg National Military Park – public lands the whole way, wooded and peaceful and without ‘No Trespassing’ signs. If you visit the park and climb the lookout tower at Culp’s Hill you may be able to see the creek snaking along just to the east, quiet and placid.
As seems to be typical of diabase rapids, it’s all or nothing. The creek is calm save for one steep little rapid until you’re about ¼ mile from the route 97 bridge where - you guessed it - the bottom drops out. The crux drop comes up quickly, an easy 4-foot ledge. Actually the rapids are only moderately steep for a creek this small and they certainly weren’t pushy when we ran them. But boy are they tight, continuous and a heck of a lot of fun. A slot here, a slot there, a pinball boulder garden, a scrapey pour-over, more slots, more boulders. Then it’s over all too soon! It’s really only one 200-yard long rapid, but it’s a good one!
Enough with the diabase already, what about the lower creek, the one that I passed up for years and years even though it is only 40 minutes from Harrisburg? Well it’s a good little run for my money. Right after the route 97 bridge, you pass a cement plant that Ed complained about, but it was quiet when I boated through. Soon you pass under busy route 15 and then the creek loops around and slams up against the highway. But once you get far enough away to not hear the road any more, things get nice and peaceful.
I enjoyed the scenery along Rock Creek. There are no cottages like those that line lower Marsh Creek. It’s all rural, mainly trees and fields. And rocks! Yes, lots of rock. Not diabase, but layered shale sometimes red in color. You see it sloping into the creek or piled up in little cliffs. Never spectacular, these little formations are nonetheless eye-catching and are very prevalent. I would guess some type of rock formation is present for 50% of the 10 mile trip to the confluence with Marsh Creek! Short cliffs swap from river right to river left and back again as the creek turns and bumps into them. At one point cliffs form a wavey wall of rock jutting from the water on river right that runs on for nearly a half mile!
While the rocks are nice the water is not. After the diabase, there is nothing that even suggests a rapid. Rock is wide for a little creek, and flat and slow. Many times I thought I was paddling through an impoundment, but there are no dams.
Take out at Mason-Dixon Road bridge or continue past Ed’s recommended Harney Road takeout on the Monocacy. Last time I was at the Harney Road bridge the only possible place to park was posted.
So little ole’ Rock Creek proves itself to be like other diabase laced streams in the Piedmont in that it has a Jekyll and Hyde personality. Like Conewago east or Marsh, you can choose a whitewater or flatwater run and have at it. Both my runs down Rock were with the Monocacy gauge at Bridgeport reading between 5 and 6 feet, falling fast from a previous day’s high of over 8. I’d have liked to hit the diabase section with the gauge peeking but that would have involved rapid escape from work and a fast charge down route 15.
Copyright © 2005 Pat Reilly. All rights reserved.