Well, there you are. He manages to manipulate "hundreds of tons of dirt and rock" and then move a steamcrawler (which, according to Wookieepedia, is equipped with turrets and large headlamps and was the basis for the Ground Assault Vehicle; all of this is to say that it is, presumably, a large object), though not at the same time.
Manipulates is a strong word - he essentially shoved the already collapsing foundation and then when the "hundreds of tons of dirt and rock" met up with lava (Which noticably slowed its momentum), he rode the earth 'crest' of the wave down until it reached the steamcrawler. He then stabilzed the rubble which had already lurched to a halt.
This passage has been regurgitated in these forums but not properly analyzed. Even I had to reread it many times and clarify with another to really 'get' the meaning behind the passage. Let's take a closer look:
A new tremor from the eruption shook the dirt cliff under his feet. He felt it sag: undercut by the river of lava, the shaking was rapidly destroying the cliff's structural integrity. Any second now it would collapse, sending Mace down into the river, unless he did something first.
The something he did was to reach deep through the Force until he could feel a structure of broken rock ten beters below him and five meters in from the face. He thought, Why wait? and shoved.
The dirt cliff shook, buckled, and collapsed.
^ This illustrates how Mace must do something or be thrown into the river. His initial intention is not stopping the landslide, but not dying in it. He decides to push the foundation of the cliff so that he can instigate the inevitable, and thus be prepared for it. His first motion is to push an already collapsing foundation. I'd imagine even Anakin or Obi-wan could muster this.
With a subeterranean roar that buried even the thunder of the eruption and the clamor of the steamcrawler's laboring engine, hundreds of tons of dirt and rock poured into the growing river of lava, organics bursting into flames that the growing landslide instantly smothered as it built itself into a huge wedge shaped berm of raw dirt across the gully; as lava slowly bulged and climbed the upstream face, the down-stream side of the cliff continued to collapse, piling over cooler lava that hardened beneath it, pushing the hotter, more liquid lava into a wave that washed around the steamcrawler's side, welled to the lip of the precipice, then plunged in a rain of fire upon the black jungle far below].
^ The first part underlined for emphasis, but I'll break this down piece by piece.
Organic material present is burnt to a crisp; the dirt itself by sheer mass begins to span the gulley of lava.
"it built itself into a huge wedge shaped berm of raw dirt across the gully"
... So basically the wave of dirt Mace forced into motion is losing some momentum and material into a gully filled with lava.
The latter part indicates that the collapsing cliff further filled the gully and buried some of the lava, while it pushed the hotter lava stream ahead of it as it solidified. The lava is explicitly shown streaming past the steamcrawler and moving onwards.
The landslide built into a wave of its own that filled in the gully as it rolled down toward the steamcrawler and the screaming, sobbing children- and on the very crest of that wave of dirt and rock, backpedaling furiously to keep from being sucked under by the landlide's roll, came Mace Windu.
^ So here we see that after the initial batch of dirt and rock sinks into the lava-filled gully and part of it not impacted by this carries on in a landslide. The landslide then streams towards the steamcrawler, with Mace struggling to not get buried.
Mace rode that crest while the wave sank and flattened and finally lurched to a halt, its last remnants trickling into a ridge that joined Mace's position with the corner of the steamcrawler's cabin. Nearly all his concentration stayed submerged in the Force, spread throughout the slide, using a wide-focus Force grip to stabilize the rubble WHILE he scrambled down to the steamcrawler's roof.
^ Here's the important part - the wave comes to a stop at the steamcrawler's cabin, and only at this point is Mace's Force powers explicitly shown to be in effect. After the stop of the wave which he realized he could not control (Hence why he instigated it rather than held it in place at the top of the cliff), he then stablizes the rubble. This is a far cry from he "controlled tons of rock and dirt with the Force LOL'.
So basically Mace's great claim to TK fame is holding dirt together once it's already stopped. Mace Windu does not stop the wave, thus he is not exerting TK force enough to control that amount of weight. Once the the momentum is spent, he can then exert barely enough control to keep it from collapsing back into the lava. Gravity itself is holding the majority of the weight down while he stabilizes the top.
So again, why are we appauding this TK as 'far superior'?
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What we see here is that Makashi is generally accepted to be the ultimate form to use in lightsaber combat; the most refined, efficient, and perhaps practical discipline when dueling against an opponent. On the other hand, Juyo/Vaapad is constantly referred to as the most demanding of all forms and that "only high level masters of multiple forms can achieve and control this discipline." Mace is a master of Juyo and the creator of Vaapad; two disciplines that Count Dooku is not known to possess.
Vaapad is considered the most demanding because of its skirting the Dark Side with its usage. It requires extreme mental discipline to not 'give in' to the rush of battle, as demonstrated in Shatterpoint. However, this doesn't immediately make it better than a fighting style deliberately made to overcome other Jedi. Keep in mind that while Mace Windu was developing and finishing his style, the Sith hadn't been seen in over a thousand years. He is shown to be incredibly instinctual in combat and great at improvising in unusual situations, as demonstrated in Shatterpoint, but even when he had more or less perfected his fighting style, Dooku still beat him.
Additionally, none of the other forms comes close to Makashi for sheer technical ability. It is the penultimate lightsaber form, and pretending that a varied proficiency of styles deliberately made for other uses (blocking or reflecting blaster bolts, channeling your emotions, fueling your abilities with the Force, etc.) is somehow superior is missing the point, or confusing "quantity over quality". Dooku does not "possess" Vaapad because it is a specific school of Juyo taught only by Mace. This doesn't mean he's incapable of defeating it, as he has already done so once before (According to the New Essential Guide to Characters, if I'm not mistaken). Mace's lack of knowledge in Makashi, however, could be a problem. Since Dooku's style is specifically made to defeat other lightsaber opponents, he specializes in the very thing they're both being judged on here. Mace's style is all about him expressing himself and learning to be adaptive. And it's a wonderful style. It's not the best style for all lightsaber fights, though. And it does not elevate his skill above a renowned master who has... wait, did I mention this already? Defeated him before.
Even Dark Rendezvouz implies that Mace being on neutral ground with him is a possible match for Dooku, not that the Jedi Master is clearly equal to or better than Dooku in combat.