Author's Note
This is my first attempt at a one-off! I hope you enjoy it! This is something I wanted to read, so I wrote it.
EDIT: At the suggestion of a few readers, I've made some changes to how the story flows. Hopefully this is better! 
Sidetracked
Sidetracked
Rarity gazed out the window of the sparsely populated Friendship Express with a slight smile as the scenery rushed by, slowly morphing from the lush, beautiful green around her home. The pure white unicorn admired her reflection as she nonchalantly flipped her fabulous purple mane with a wave of her glistening hoof. “I do so love travelling by train,” she half whispered to nopony in particular. “The view from the window is always so breathtaking.”
The colorful train of purples and pinks had left Ponyville station about 15 minutes before, headed to a place she knew nothing about. She'd never been to “Whitherston,” but the gloriously glowing map in Twilight's absolutely fabulous, sparkling castle had decided she and her friend Applejack would be going there in order to solve a friendship problem.
She'd been in her inspiration room, just finishing up the designs of her new clothing line when her flank suddenly felt different. At first she thought it might be the stallion over whom she'd been drooling through the window, but upon closer inspection found it to be Twilight's friendship map calling.
She'd arrived at the castle to find that Applejack had also been called. Now the orange earth pony was seated across the aisle from Rarity, munching on some apple-related snack or other. Rarity could smell the aroma of apples. 'Twas pleasing to the nose, to be sure, but not quite so pleasing to the eyes as they watched her friend wolf down the pastry, a little even splashing up onto the cowpony hat atop Applejack's blond mane.
Applejack seemed to notice the look of disgust into which Rarity's face was currently scrunched and laughed. “You should see your face raht now, Rarity!” the earth pony quipped as Rarity's eye started twitching and her hoof was pointing to the spot of pastry on her friend's hat.
Applejack seemed to notice where Rarity was pointing and pulled down her hat to clean it off. “So what sorta problem d’ya reckon we're goin’ ta solve this time?” she casually asked as she flicked the sticky crumbs.
Regaining a modicum of her dignity, Rarity flicked her mane and replied, “I haven't the foggiest, darling. Though I do hope that this doesn't take long. I'm due to have my new line in Canterlot by Sunday!”
“And today's Wednesday,” Applejack finished. “That sure don't leave a whole lotta time fer you ta finish whatcha got goin’.”
“No, it certainly doesn't,” Rarity agreed. “And while I do take my role as an Element of Harmony in preserving friendships very seriously, I also have deadlines to meet!”
Applejack paused a moment before responding. “I know you said it's s’posed ta be in Canterlot by Sunday, but what sort of a thing’s gotcha in such a tizzy this time?”
“It's a fashion show, darling.” Applejack wore a wry grin as her eyes rolled, but Rarity continued. “It’s not even a very large show, but it is one of my favorites. As much as I absolutely adore the larger shows, with all the wonderfully gifted ponies and all their fabulous ideas, I also love to support the smaller shows, and this one is one of the best. It's mostly the up and coming designers who've yet to get into the more prestigious shows. I try to take a new line every year to help inspire all the ponies there.”
“Well, gee, Rarity, that's awful nice o’ yeh. I bet some o’ them ponies are just tickled pink as a hog to have you there.”
The two chatted like this for the rest of the train ride, the number of other passengers slowly waning as their trip continued on. Once they were past Dodge Junction, they seemed to be the only passengers left on the train.
Once they had arrived at their intended destination, Rarity and Applejack grabbed their luggage and disembarked the train. As she came down the steps, Rarity began to feel very odd. It was a familiar kind of odd, and she wasn't sure she liked where this was going.
Also, she didn't like what she saw in front of her. Before her view stretched what appeared to have been a town at one point in the distant past. The wooden buildings were old and rotting, and many appeared to be nearly collapsed.
As this sank in, she heard the train start to pull out behind them as she noticed the tumbleweeds that seemed ubiquitous to this area of Equestria. They were everywhere, and much more so than ponies, it seemed. In fact, outside of herself and Applejack, there didn't seem to be a living pony as far as the eye could see.
Once the Friendship Express had pulled completely out of the station, Rarity felt a familiar warmth at her forehead. "Ah, ponyfeathers,” she cursed aloud, much to Applejack's apparent amusement. Then the world seemed to slant to the left as her hooves’ connection to the ground faltered and she felt herself magically dragged to the right.
This had happened before, of course, but never in the middle–or at the beginning–of a friendship excursion. The worst part was, there was nothing she could do but wait it out. “Applejack, darling!” she called. “Be a dear and follow me?!”
Applejack just grinned and trotted along behind–or, better put, beside–her. “So, uh, how often does this usually happen, there, Rarity?” the earth pony asked with a grin.
Rarity's only answer was a huff and a scowl, which stayed on her face for the entire trip as she was dragged from the train station, her hooves dragging in the dust and dirt, kicking up a cloud as they did so.
Then it was rocks, some of them as tall as she was. For a horn that had no eyes to see where it was going, it seemed to have an affinity for throwing the body to which it belonged into all the large rocks it could possibly find. “Oof! Ow! Aah!” she screamed as she hit rock after rock.
Then she hit the cactus field. Everywhere she looked–which was in one direction, as she currently had little control over her own movement–there was nothing but cactus. "Oh, horseapples,” was her only commentary.
Through all of this was the almost constant sound of laughter from the left. Honestly, had their positions been reversed, she would probably have done the same thing Applejack was doing, though she would have at least tried to have been more discreet about it.
When she finally came to a stop, Rarity's horn had knocked her head into the wall of a cave entrance. “Ow,” she mumbled again, rubbing the latest in a series of sore spots with a hoof. Applejack's chuckling didn't make it any better.
Looking around, however, Rarity first saw the cave and the seemingly endless blackness that awaited inside. Then her eye caught the sparkle of a gem. She cast a light spell, lighting her horn, and cautiously walked inside.
As she approached, more and more gems caught the light cast from her horn and reflected it back in a veritable rainbow of different colors. There were red gems and orange gems. There were yellow gems and green gems. There were blue and indigo and violet gems. There was alexandrite and opal and zircon. There were types of gems of which Rarity had never heard nor seen.
This was the treasure trove of treasure troves of which she'd never dared to dream.
Even Applejack behind her seemed duly impressed, as she let out a low whistle. “Wow, Rarity,” the farm pony breathed. “That's… That's beautiful.”
“Very much so, my dear,” Rarity whispered, still almost breathless at the sight. “Ponyville's own gem cave is nothing short of spectacular, but this…” She sighed contentedly. “This is magnificent.”
Then she turned so fast, she felt a hint of dizziness. “APPLEJACK!! WE MUST GET THESE GEMS TO PONYVILLE!!” She felt her face contort as the words left her mouth with much more volume than was necessary, but she didn’t care. Several of these rare gems were exactly what she needed.
“Eh, heh heh,” her friend replied, “but we don't have nothin’ to carry 'em with.”
“Did it look like anypony actually lived in that town, my dear?” Rarity replied a little dreamily, now gazing back toward the gems. “We can probably take the wood from the buildings and make carts to pull what I'll need back to the train station. And don't worry about our fare home, darling. With the bits I'll earn from this, I can afford the luggage costs for a couple thousand pounds of gems.”
“But, uh… what about the ‘friendship problem’ we're supposed to be solvin’?”
Rarity just scoffed. “Oh, pfft, keh, fuh. Which is more important at the moment, darling; some squabble between friends that they'll probably figure out anyway, or this cave full of priceless gems?!” Her eyes sparkled as much as she could manage.
“Uh, Rarity? You do know who yer talkin’ to, raht?”
Rarity stopped at that and shrugged. “Ugh. Fine,” she replied, somewhat disgruntled. “We'll fix this ‘friendship problem’ and then haul all these precious little new friends of mine home in time to finish the dresses for the fashion show.”
