Now, this ramble probably won't be as in-depth as my ones on the other elements (since right now, I'm mainly stalling for time, waiting for my mom to get off the desktop), but I still want to cover the wide variety of subjects Earth has to offer.
Of course, not all of this gets featured in Red Hood Rider. While the elemental rider of Earth is akin to the actual AVATAR of Earth in strength (at least, Sally is: canonically, the current generation of Riders is the ONLY generation of Riders who can fight the elemental avatars in a duel to a draw; all other generations either mutually back off after a day or concede defeat), this does not mean the rider will actually USE every ability at their disposal.
...That generally applies for all the riders for that matter. They're virtually gods in theory power-level wise. I'm not sure if I ever posted, or even wrote up, this tidbit, but somewhere along the line, there proved to be a slight need for an explanation in their abilities.
Namely: I decided from the get-go that the Elemental Riders' base powers were set in stone: they could not suddenly develop a new power out of nowhere. All they could do is learn to use their existing powers in newer, more creative ways, which continuously become more and more imaginative with abusing wording and loopholes, e.g. taking something meant as a metaphor and using it literally, or using something that was meant literally as a metaphor and then applying that metaphor to a new concept.
Then I created the concept of magical fatigue and even had riders be limited by it: Ruby's powers shut down because of it, and Vili's growth runs into the problem of it, for a start. So, my solution was as such: Riders gain new powers as they learn to be creative, often inspired by seeing other powers. (For instance, if someone else uses a really cool technique, then they'll try to figure out a way to replicate it with their own powers, which requires different rules.) As such, their basic powers never change...
...HOWEVER, while their basic power never changes, they cannot instantly use god-like powers because of magical fatigue. They have a limit to what they can do, off of their storage of magical energy and ability to draw in magical energy. This limit DOES grow with experience, training, practice, time, and age: in other words, the older and more experienced the Rider, the higher their magical fatigue limit becomes, effectively allowing them to do more. So, that godlike ability which they couldn't use before, they can maybe use later...especially the more in-tune they get with their powers.
All that said: even at the peak of their powers, they're not going to imagine every POSSIBLE application of them (heck, even I can't and I know more about these elements than anyone else!), and even if they could, it's not like they necessarily have a plot-relevant usage.
So on that note: Earth is by far one of the strongest, most versatile elements. Every element except darkness and ice have ties to life, which includes earth. (Light has ties to life in the spiritual sense. Water has ties to life in the practical sense. Fire has ties to life in the metaphorical sense. Air and Energy serve as vessels for life, with Earth being life in a physical sense.) This gives Earth users the strength and harmony of their surroundings. Earth is also such a large element, covering so many things, that it is often subdivided into four separate elements, something unique to it and it alone as an element.
In this case: Nature, Rock/Stone, earth (as in, generic ground, like soil, sand, etc.), and Metal, with Metal being the hardest form of Earth to master and Nature being the most diverse. (Nature itself can be subdivided into 'plant', 'living', and 'other', with other covering things like gasses, acid, poison, and the like.)
Because of its many areas, Earth has a great many number of subjects tied to it. It is, along with Energy, THE defining element of Endurance, both physical and mental. It is associated with being tough, honest, kind, yet also blunt. It is up there with Water in healing abilities, especially regenerative, and can cover that subject from multiple angles, including how to shut down an existing regenerative factor. (Something it is second only to Darkness in ability to do.)
This is why Sally is virtually impossible to defeat: her stubborn refusal to accept defeat allows her to survive any encounter, requiring the utmost of extreme circumstances to so much as STUN her. Her particular fighting style emphasizes the power of the Earth, drawing largely from the subjects associated with Rocks, the core strength of destructive power, but she does incorporate some of the smoother, softer elements of Nature into her fighting, via her threads. She also can use her talents to help herself or other Riders, via her mastery of these things. For instance, she's a master chef, able to cook up any meal to its ideal state, and is great at figuring out solutions to peoples' problems.
It should also be noted that Earth covers 'magma' as well: it's VERY unusual to see an earth-user be able to manipulate magma, even rarer than it is to see them manipulate Metal (most who manipulate Metal are trained in using that specific sub-element rather than being generic Earth users), since it is something more commonly associated with Fire.
Fire users can ALSO manipulate magma, for that matter, but Earth users can too. It's just liquid, molten, hot earth, after all, and is closely tied TO metal for that matter. (Because metal is just refined stone, and stone is part of the earth, and when metal is melted, in its molten state...it's still metal, still earth, in spite of being fiery.)
Soyeah, that (along with it also having shared control of Gravity) is a basic rundown of Earth as an element. Told you it wouldn't be AS in-depth as most examples, because I'm really making broad, open statements here deliberately. The idea is for people to see the elements as really, really flexible, but still following set guidelines.
They can't do anything, but can do almost anything if the user is clever enough to figure out how, and has the necessary strength to pull their intended feat off. (Basically: while every user of an element has the capacity to, in THEORY, use any aspect of the element, in practice, nobody can master EVERY aspect of the element. Most can't even become proficient in the element as a whole. They just become very good at making it do what they want it to.)