In Baltimore, where the Jones Falls canal lets out into the Inner Harbor, there is a long, low, white-painted, rust-spotted railing. I have been using it as a balance beam since the summer of 2014. The v-shaped scrapes at each end show how far skateboarders get when they use the railing as a grinding surface. In the autumn of 2015, I started coloring as a hobby--and suddenly began to see the railing-patina in detail. Since then, I take photos whenever I notice new marks. My friend Chip York characterizes this as "temporally shifted and anonymously collaborative urban performance art". Some skateboarders call the marks "coping trails" or "grind business", according to answers to a question I posted on Facebook. Two local skaters who I met in September 2016 call them "History." The scrapes are made by the board's trucks; some of the color streaks are from wheels, but most are from graphics that people use to decorate the undersides of their boards. At first I was simply taking pictures of pretty colors, but this work has evolved into a meditation on time, growth and decay, effort, cause and effect, material culture, the way new creative energy is transforming Baltimore's industrial history, and how art happens. I'm into it. There are well over a thousand photos in the series, which is more than most people want to look at. The images in this "best of" gallery are special in some way; they are someone's favorite, or the weather was unusual, or some new marks had appeared. [Everything in this gallery was shot with an iPhone (4S until Sept. 1, 2016; then an SE.) I have used no physical or digital filters. Images are unmodified except for cropping/scaling/rotation/enlargement.]