En echelon or in abbreviated form in this knowledgebase, 'echelon' joints, are closely spaced sub-parallel joints arranged in echelon pattern. Members or segments in echelon geometry can be under-lapping and over-lapping (top row of Figure 1) or right-stepping and left-stepping (bottom row of Figure 1).

Figure 1. Echelon patterns of joints. Under- and over-lapping patterns in the top row and right- and left-stepping in the bottom row.

For example, the photographs in Figure 2 and Figure 3 illustrate echelon joint trace geometries on a glaciated surface of granodioritic rock and on a limestone pavement, respectively, both generally in a right-stepping configuration.

Figure 2. Echelon joint traces on a nearly horizontal glaciated surface in granodiorite outcropping at Donner Pass, Sierra Nevada.

Figure 3. Photograph showing a joint zone made up of highly overlapped echelon joints in limestone exposed on a relatively flat river bed, Taughannock Falls, NY.

More complex geometric arrangements occur in joint zones with a large number of individual members as illustrated in Figure 4 which is a map view of at least three sub zones with different geometric properties on a sandstone pavement.

Figure 4. An array of quartz veins, only one of which is continuous for the entire width of a sandstone pavement (about 20 m). All others are short discontinuous traces forming mostly left-stepping echelon patterns, south of the Shannon River, southwest Ireland.

Figure 5 which is a three dimensional view of a complex zone in limestone exposed in a road cut.

Figure 5. Outcrop photo showing three dimensional geometry of an echelon joint zone, in limestone, South Central Texas. The joint zone is labeled in the photo. From Wilson et al (2008).