Yup! Slate chips from Amazon (I use a couple different sizes to create a varied effect, but they're all the same brand).
Superglue them to the base, wash them with a heavily watered down 2:1 ratio of flow improver:Skrag Brown. Then drybrush with Ryza Rust, followed by a drybrush of Eldar Flesh.
The bigger rocks are some slate pieces I got from a little mom and pop shop... something about rivers: https://www.amazon.com/gp/product/B072DW7NC4/ref=ppx\_yo\_dt\_b\_search\_asin\_image?ie=UTF8&psc=1
There are autumn leaves that work well, as well as grass tufts that look more winter season available from various places. Add some Vallajo basing paste, maybe some slate stone and that's one way to do a pretty simple autumnal base.
Apologies up front for the lengthy list.
I usually do large batches of bases in a variety of sizes through step 10 so they're ready for me when I finish any particular Dark Angels minis. I use basically the same process for other 40k / Kill Team bases, just changing the specific colors I use for drybrushing and the base rims.
EDIT: I forgot to mention, everything I mount to bases gets pinned and glued. I refuse to rely on just superglue to hold things down.
Amazon. Natural Slate Stone - 1/4 to 1/2 inch Slate Gravel for Miniature or Fairy Garden, Aquarium, Model Railroad & Wargaming 1lb https://www.amazon.com/dp/B072DW7NC4?ref=yo_pop_ma_swf
Amazon. Natural Slate Stone - 1/4 to 1/2 inch Slate Gravel for Miniature or Fairy Garden, Aquarium, Model Railroad & Wargaming 1lb https://www.amazon.com/dp/B072DW7NC4?ref=yo_pop_ma_swf