compaction and good construction techniques, trails that have gentle gradients, and/or bedrock tread material were observed to be relatively resistant to erosion and have few erosion problems. Some trails, however, were constructed with poor grade and alinement characteristics on areas with soft soils. Rill and gully networks were observed on steeper trails with the same degree of compaction as shallow gradient trails.

Rills are common on steep trails throughout the park and are usually associated with improper drainage or drainage structures that have not been maintained. Rills form in places where surface runoff cannot exit off the trail, forcing the water to concentrate in low spots and flow down the trail. After the water erodes through the compacted surface layer, rill development accelerates. Rills that are left untreated for many years develop into rill networks, and in extreme cases become gullies. Local shallow bedrock conditions on steep and flat trails can contribute to their relative stability and resistance to rill development.

The erosional impacts identified during the field inventory were related to natural processes including slope instability, rainfall, and surface runoff, as well as recreational trail use including running and hiking, horseback riding, and bicycle riding. Individual erosion features documented in the specific areas of concern are presented in Appendix A, which includes descriptions of the physical parameters measured, field sketches and photographs. The total volume of past erosion that has occurred at each feature observed on the trails and watercourses is presented in Table 1. Approximately 59% of the total past erosion is attributed to naturally occurring bank failures and landslides observed along watercourses. This volume is considered a minimum because the volume of older healed bank failures and inner gorge landslides is difficult to calculate. The most common erosion feature in Joaquin Miller Park is rills created by surface runoff. This erosion, however represents only 7% of the total past volume of erosion.

Areas "A, B, C, F", and "G" (Figure 1) have minor evidence of erosion. Bishops Walk and Sinawik Trail within areas "B" and "C", respectively, have shallow bedrock conditions that are resistant to natural and recreational erosion. These two trails do not have erosion problems associated with drainage or recreation. The Sunset Trail within area "A" is relatively flat, well compacted, and relatively resistant to erosion. North of Sinawik Cabin the Sunset Trail traverses the southeasterly facing slope of Palo Seco Creek canyon. This portion of the trail is cut into a steep hillside and is vulnerable to landslides. Presently, there is a small pile of rocks and debris that has been deposited on the trail from a cut slope landslide. This material can easily be removed by a shovel crew and is not considered a major problem. The Sinawik Trail and Lower Palos Colorados Trail parallel each other on opposite banks of Palo Seco Creek in the vicinity of area "G". In places where these trails are next to the creek, high flows have caused bank erosion (erosion features 2, 3, and 3A). Area "F" includes the upper portion of the Wild Rose Trail and its junction with the Sequoia Bayview Trail. The upper Wild Rose Trail traverses a redwood grove and is relatively flat. This portion of the trail had no signs of significant rill, gully, landslide, or recreation-related erosion.