Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 206. The Chesapeake and Ohio Canal National Historical Park offers an opportunity to examine most of the rock formations and geologic structures typical of the Potomac Appalachians as well as many features of civil engineering related to the C&O Canal. This can be done in a safe and leisurely manner along the canal towpath. Several plants along the canal are to be avoided. Poison Ivy growth is rampant. The plant grows as low ground cover, as a bush and as a vine. Poison Ivy is characterized by leaves in clusters of three. Contact of the skin with the plant or with its secretions on clothing, shoes and other personal objects can result in a severe skin irritation that lasts up to a month. Another annoying plant is the nettle. On contact, even where the skin is covered by clothing, this plant can inject a toxin that numbs the skin for several hours leaving a persistent itch for a day. During the warm season ticks, which carry spotted fever and Lyme disease, are common throughout the area. It is prudent after being in the field to make a careful check to see if ticks are on the body and remove them. Two poisonous snakes are in the region. The Timber Rattler is a dangerous viper but is seldom encountered. It is not aggressive and generally moves off unless cornered or surprised. It occurs mainly in sandstone areas. The Copperhead is common in all parts of the area. Its bite causes injury but it is seldom fatal to adults.