Though Tectonic forces about 2–3 million years ago caused the terrain to rise across the Monument Upwarp in southeast Utah and northeast Arizona, the river maintained its course as an antecedent stream. The Monument Upwarp consists of a series of parallel anticlines and synclines running generally north to south in an area roughly long and wide. Where the river passes through these formations, it has sliced deep canyons through the distinctively reddish rock. In places, the San Juan has entrenched its ancient meanders thousands of feet into the bedrock, as can be observed in Goosenecks State Park, where it winds through a set of horseshoe bends while traveling a straight-line distance of only . The canyon cutting was accelerated during the Pleistocene Ice Ages when the climate of the area was much wetter. The wetter climate resulted in floods of up to –ten times larger than any flooding of the San Juan in recorded human history.