For EARTHQUAKE/GROUND MOVING/GEO-SHIFTING/PROGRESSIVE TEXTURE-type sounds – really, just about anything that could use more organic movement:
Go to the supermarket and head straight for the bulk foods department. Get ample bags of different snacks/grains — there is a huge variety of texture to be found. For example, cashew nuts have a nice clunky grit to them. Trail and Oriental mixes of different particulate compositions can have versatile tonal colors. There are certain gummy sweets that are more subtle but nonetheless add flavor and weight to other elements.
Then when you’re back home or in your studio environment, put on a pair of food safety gloves (if you intend to eat this stuff afterwards), and try recording different gestures, even pouring them into an absorbent bowl/container, shuffling them around with your hands. Monitor carefully to build upon what “sounds good” — note that some combos don’t tend to work too well, like rice in a glass bowl can sound very “clinky” and annoying to the ears. Ye olde usual “experiment until you find something you like…” applies here.
Afterwards, you can pitchbend things (usually down) as-needed to create desired effects. It can also be very aurally rewarding to use granular synthesis to process real-world grains, and build up layers of textures that can be mixed to taste (literally).
This is how I did most of the Terrain Editor sounds for our virtual reality platform Sansar, with multiple tracks of manipulated grains, and you can hear a bit of it in action @ fmod.com at the top, a few seconds in. :D