When people think of Oregon they tend to think of rain, a sort of never-ending rain, over forty inches a year on average. But eastern Oregon is all but a desert, receiving a third of Portland’s average, and some of Oregon really is a desert, with less than ten inches of rainfall a year.
This low level of rainfall exposes the ground and the ground can tell its story, the story of rains from the distant past.
The red is from a time when the hills here were warm and wet, as wet as Portland is now, and volcanic ash fell from the sky, brining with it all that iron. As the rainfall decreased over millennia the soil records that decrease, the soil now yellow.
The black bands are a bit of an oddity, colored by manganese, and may tell a story about the difficulties experienced by the life here. One possibility is that the manganese became concentrated in pools as the climate dried, another possibility is that certain plants may have fixed manganese in the soil. The candidate plant suggested by the people who write the signs for the John Day Fossil Beds National Monument might be akin to the “Kenyan Toothpick Tree” which is used by the local people in Africa as a famine indicator, because the tree grows new shoots and flowers when experiencing unusually dry weather, and who eat the fruit from the tree during these times as a “famine food.”