Ichnofossils, AKA trace fossils, in the sidewalk on the summit of Lava Butte. Of course, since the concrete is a man-made material, it's a pseudorock, and these are pseudofossils. Whatever. These are likely impressions left by a golden-mantled ground squirrel, which are very abundant and common in central Oregon, especially in relatively wild areas with a heavy human presence. They are very clever beggars, and can be quite bold about approaching people for handouts. They're tough to resist, but we don't help them by feeding them.