Barker Dam -- located in the central part of Joshua Tree National Park -- was originally constructed in 1902. The dam was essential to ranchers and homesteaders settling the area. Seeing as the desert is without natural springs, the dam's water levels were a matter of life and death for these people. Barker Dam's historic significance landed it on the National Register of Historic Places since.
The modest 1.5-mile loop to the dam made it one of the more popular hiking destinations in Joshua Tree. However, in February of 2013, the trail was closed to visitors. Why? Graffiti artists spoiled the fun.
Lowering water levels from California's drought exposed parts of the dam walls, and graffiti soon covered nearly 50% of the walls. It was not only tough on the eyes, but also caused physical damage to the concrete holding the dam together. Luckily, some conservationists perfected a method to remove the graffiti and restore the dam to its former glory. I'll let them go into more detail:
[University of New Mexico] conservators employed a method known as "in-painting" to blend the scratched areas into the surrounding naturally weathered surface. After testing a variety of different methods ranging from dry and wet brushing, to low-pressure power-washing, and various types of paints, the conservators settled on silicate based paints for their durability and the ability to re-treat these areas in the future without having to remove the current treatment. "In-painting" is a time consuming and labor intensive process that involves adding pigments to the scratched areas with a method similar to the painting style of pointillism. Instead of merely painting over the graffiti entirely, the paint is applied in a way that matches the surrounding colors, textures, and patterns.
Visitors can once again visit the dam. And if you make the hike and notice someone scrawling their name on the dam, you have my permission to give them what-for.