During our dog walks I get the occasional geology lesson. Who knew there was so much geology going on in Pasadena? My god, it's happening all the time, right under our feet!
About this photo, Becca says:
"This is a nice example of graded bedding. When water flows through the stream channel it transports material of various sizes. Fast-moving water transports relatively large sediment such as boulders, cobbles, and/or pebbles. Slow-moving water only has the energy to move small sediment such as sand, silt, and/or mud. Imagine taking a jar filled with water and sediment of various sizes, shaking the jar and placing it on a table. The larger sediments will settle to the bottom first, and as the water current in the jar continues to decrease, progressively smaller sediments will settle on top.
"As a side note, if these sediments were buried and left undisturbed, they could go through a process called lithification and turn into a sedimentary rock. And then, my friend, this beautiful graded bed would be preserved in the rock record!!"