Our first stop in Northern California was the Lava Beds National Monument, a series of tubular caves carved out by lava flows about 30,000 years ago. We spent a whole day spelunking through all the green circle and blue square caves within a few miles of our campsite, and even braved one black diamond.
Most of the time we could walk comfortably through the caves, with the occasional crouch or duck-walk to squeeze through a shorter passage. It was an amazing experience to wander pitch black caves hundreds of feet long, barely seeing any other visitors all day.
We also got our first taste of desert camping.
Next we visited Shasta Lake and the nearby caverns, which were lined with unending stalactites, stalagmites, and crystal formations. Since a guided tour was necessary we did not feel the same sense of adventure, but still marvelled at the geological formations that took thousands or millions of years to form.
On the way to Shasta Lake we made a quick stop at Burney Falls. The streams feeding this waterfall exist mostly underground, with only some of the water surfacing upstream of the falls. Other currents can be seen coming directly out of the rock face.