“Friendship, Hermes. You’re almost through the southern gap. Now turn directly east if possible. That’ll aim you towards the center of the main channel of Mawrth Vallis. Please acknowledge, over.”

Starlight Glimmer, seated next to Fireball in what had been Amicitas’s co-pilot seat, keyed on her microphone. “Friendship acknowledges, roger wilco, over.” Switching her headset from the ship radio to her suit’s magic-powered comms, she said, “Confirmation from Hermes, Mark. We’re in the valley. The main channel mouth is due east of us.”

“That’s what I figured,” Mark said from Rover 2’s cabin. “Cherry, did you get that?”

“We copy, Mark,” Cherry Berry’s voice added. “We’re clearing a couple of large rocks out of the way now, but the ground is wide open once you get past that last narrow part of the pass.”

Ten days of very easy driving across the northern lowlands of Mars had come to an abrupt end towards the end of driving the previous Sol. This hadn’t been totally without warning- NASA, via Johanssen on Hermes, had warned them- but it had still been a bit of a shock to see the big-ass mountain of flood debris dead ahead, where the low-resolution map in the rover computer showed a wide open valley entrance.

They’d parked close to the mountain and taken some pictures. NASA couldn’t decide if the great mountain that spanned almost the entire mouth of Mawrth Vallis was debris left behind by subsiding flood waters or the moraine of some long-gone glacier. They’d have to wait at least another forty sols to find out, but they’d sent Mark and Fireball out to get enough photos and video to keep the astrogeologists arguing for years.

As a consequence, the Whinnybago had made a late start of it the next day. Partly this was due to the shadow of the mountain blocking much of the early morning light, but mostly it was due to waiting for the broadcast window to Hermes to open so the crew could get guidance, even at eighteen minutes’ round-trip lightspeed delay, from Hermes, its superior Mars maps, and its direct connection to the Martian orbiter network.

Their eyes in the sky had revealed the southern pass between the mountain and the outer edge of the ancient valley mouth, though tight and half-filled with loose debris, was the more direct route around the obstacle. The northern route was twice as far and not that much more open, according to Johanssen. Unfortunately the difference might still have been moot, since a ten kilometer drive had taken an hour and a half, counting the time lost waiting for updates from Hermes.

But that was over- or almost so. “I see the tight spot you warned me about, Cherry,” Mark said. “Fireball, prepare for plus thirty on my mark… now!”

“Plus thirty,” Fireball rumbled, turning Amicitas’s flight yoke to the point marked on the steering guide Mark had installed.

“And zero!”

“Zero,” Fireball said as the rover crept cautiously past a boulder so large the top of it rose almost level with the former spaceship’s cockpit windows. “Boss, how big rocks did you move?”

“Don’t ask,” the earth pony turned forward scout replied.

“Minus ninety in three, two, one, now!” Mark ordered.

Fireball yanked the flight yoke all the way to the right. “Minus ninety,” he said.

“Hold it… hold it… zero!”

Fireball straightened. “Zero,” he said.

“Yeah, that looks beautiful,” Mark said. “Wide open now. Let’s get a little more distance from the pass, and then I’ll turn us due east and open up the throttle.”

“Which way is east?” Fireball asked. “Can’t see sun from back here.”

“Um, yeah, it’s pretty high up by now, isn’t it?” Mark said. “But I can see Spitfire’s spacesuit. It’s the only white thing anywhere in sight. Cherry, I’m following Spitfire. That good with you?”

“No problem, Mark. We’ll stick together for a while. What are we looking for?”

“An upslope. A shallow, level upslope. Starlight, ask Hermes for details, okay? By the time you get a reply, we should be eight or nine kilometers along.”

Starlight nodded to herself, then remembered Mark couldn’t see her head from the rover cabin. “Will do,” she said.

“Lot of trouble to drive up a river,” Fireball muttered from beside her.

“Less trouble than having to work it out for ourselves,” Starlight replied. She switched back over to the radio. “Hermes, Friendship,” she called. “We’re out of the pass now and making full speed due east. We expect to be about nine kilometers east from our current position by the time we get your response. Please give guidance to the best path up the valley from that position. Over.”

As Starlight switched her headset back to suit comms, she heard Mark say, “So, after all of that, are you talking to me again?”

“That depends, Mark,” Starlight growled. “Are you going to let me have my apprentice witch character?”

“Oh, not this again,” Mark moaned in her headset. “I banned all witches from the campaign because I didn’t think you’d have fun being constantly stepped on by Granny Weatherwax. If there’s a serious magic problem in Lancre and any witch is involved in any way, she’s going to take over the whole thing. She just is. That’s how the books worked.”

“They don’t work like that for Tiffany Aching.”

“I am not giving you Tiffany Aching for a starting-level character, Starlight,” Mark groaned. “Look, if you want to be a magic user, be a hedge-wizard.”

“I’m holding out for witch, Mark,” Starlight insisted.

“Dragonfly here. Just wanted to mention the total and absolute lack of rocks in the path ahead. Definite absence of obstacles of any kind for klicks and klicks. Nary a rock. Boulders are conspicuously inconspicuous.”

“Message acknowledged, Thesaurus Jones,” Mark replied.

“How much longer are we going to drive today, Mark?” Cherry asked. “We’re already an hour past the point where we’d normally stop.”

“I’m going for the full seventy kilometers,” Mark said. “We won’t start tomorrow on full batteries, but we can drive in shifts. Assuming no more major obstacles- or at least advance warning without geological detours- we should be back on normal driving schedule by the time we get out of Mawrth.”

“Pretty big assumptions, Mark,” said Starlight.

“I’m thinking big,” Mark replied. “Mars is a pretty big planet, after all.”

“If you’re thinking big, how about you think a little bigger about witches in the campaign!”

“Starlight, drop it. We’re tired of it.” Spitfire’s first words in the radio conversation were the last…

… almost.

“So, talking to me?” Mark asked.

Starlight stared silently out the cockpit windows at the gradually receding mountainside.

“That’d be a no,” Mark answered himself, and then the conversation really did die.

Author's Notes:

So, yeah. In the original book Mark talks about how Mawrth Vallis is wide open at the mouth and nice, smooth and near-level all the way up.

Take a look at actual orbiter maps, and you'll find none of that is true. The mouth of Mawrth Vallis, along the line of what obviously was the original edge of Arabia Terra, is almost completely closed off by a big-ass mountain. The interior of the valley has splits in the middle, rivulets, and one hell of a lot of boulders, as you would expect if you were looking at a river valley in mountainous terrain on Earth that one day spontaneously went dry.

That said, it's still Mark's best available option. But it's not going to be as easy as all that.