Switchbacks!

The weather was perfect! It was actually slightly cold and I put on long sleeves when we began our decent.
This hike was incredible! There was always something to see: water crossings on solid boulders, meadows with so many wildflowers and different colors, sweeping views of The Trinities, Castle Crags, Lassen Peak, Mount Shasta, Black Butte, Lake Shastina, even could see Mount McLaughlin in the distance. Crossed by several lakes, including Deadfall Lake and a few up at the headwaters.
After we crossed the PCT we began the most vertical climb with 15 switchbacks (see the picture), there were yellow and purple wildflowers dotting the mountainside.

I’m curious about the markings on some of the trees. Does anyone know what they were for (see pictures), or why they were there? My guess is that in the past there was something on those trees to mark the trail???