The bed of Fishing Creek contains red and brown shale in some places. Other parts of the watershed lie over gray sandstone or conglomerates. There are numerous deposits of iron ore, limestone and marble in the watershed of Fishing Creek. Most of the rock in the watershed, including the Trimmers Rock Formation and Catskill Formation, is from the Devonian Period, but some of the northernmost tributaries have watersheds on rock from the Mississippian Period, such as the Huntley Mountain Formation and Burgoon sandstone. The creek is a freestone stream although its water is colder than that of most eastern freestone streams.