Found this cool rock at lake Tahoe. It has 2 white rings around it that are so perfect I thought at first they were drawn. Now it lives in my Chia pet garden. Here’s an additional pic.

Found this cool rock at lake Tahoe. It has 2 white rings around it that are so perfect I thought at first they were drawn. Now it lives in my Chia pet garden. Here’s an additional pic.

Could be from one of the streams leading into the lake. Could be many, many years of the small but present waves of the lake hitting the shore. Or could have been created when the Sierra Nevada were closer to sea level.
Nice. Tahoe gets huge waves from time to time. Most of my cool rocks come from that area.
Waves were my top theory.