Outside Sada, Iraq -- As the crimson sun rolled behind the Taraq an-Naja Mountains, a group of U.S. Marines scraped their shovels across the infertile, rocky soil of western Iraq, trying to set their mortar launchers deeper into the dust.

In the Euphrates River valley before them twinkled the white and yellow lights of Sada and Karabila -- key Iraqi towns near the border with Syria controlled by fighters loyal to insurgency leader Abu Musab al-Zarqawi. Marines from the 1st Mobile Assault Platoon, Weapons Company, 3rd Battalion, 6th Marine Regiment camped out Thursday on a moonless night in the desiccated expanse overlooking the towns, setting up mortar firing positions and keeping an eye for any insurgent movement inside the settlements.

As they set up their mortars, the Marines discarded the metal bindings of 81mm ammo cases, leaving the long metal strips on the ground like some strange petrified seaweed mysteriously beached onto the Iraqi desert. On the bottom of a dry riverbed, salt reflected the receding light. A lightning flash, an early sign of fall, lit up the horizon over Sada, and a thunderclap followed.

Then darkness enveloped the encampment, and all became smells and sounds.

A Marine laughed in the distance. Another one, closer, lit a cigarette, which glowed orange in the dark. Dogs barked in Sada, and a donkey screamed. A humvee smelled of diesel fuel. A muezzin started a solemn call for the evening prayer. Somewhere, a car sped down a road. From time to time, helicopters roared overhead. Marines whispered loudly over the racket of rotors.

Cool wind carried noises across the shadowy desert, and Marines listened and sniffed in the darkness.

Night is different, said Gunnery Sgt. Derrick Link, 32, as he listened to the static on the humvee radio, a lifeline for his platoon to battalion commanders. You rely on different senses in the night. Your hearing instead of your sight. Everything sounds a lot closer than it is.

Night is also a time to contemplate and reminisce. The Marines talked about home.

Navy medic Michael Larson, 30, talked about 19th century Russian writers (I love Gogol!) and food.

I used to make focaccia bread, with olives and Parmesan cheese, he said. I'd make pasta Alfredo. I love to cook. Make the whole course.

When I go home, it will be, like, my girlfriend, food and my daughter, these three, nothing else.

Pfc. Dale Fellows, 19, talked about his girlfriend, too. She was a year ahead of him in high school in upstate New York, and now she goes to Northeastern University in Boston. She is an intern at the Boston Globe.

Link talked about his 9-year-old daughter, Samantha, who started cheerleading classes this year.

Stephen Thomson, 30, talked about his dream to go to medical school to become a radiologist.

They work in teams, and they really know their anatomy, and I'm very interested in anatomy and physiology, he explained.

At 9 p.m., desert wind kicked up dust and carried it across the encampment. The temperature dropped from the daytime's 95 degrees to 62 in a matter of minutes. Marines materialized out of the opaque darkness, stopping by Link's truck to chat, rest and smoke. Some moved on, disappearing in the blowing sand; others stayed to seek the comfort of companionship.

They rarely attack in the dark, Lance Cpl. Jared Treadway, 22, consoled himself, his shoulder-mounted launcher leaning against Link's humvee.

Link disagreed.

Last time we stayed overnight, last week, the first night we got hit pretty bad, he said, standing near his humvee, which was parked facing the lights of Sada.

But this time the troops were luckier. An orange trace of a lone mortar round arched out of Sada at about 5:30 a.m., injuring no one.

Maybe they are just waiting it out; maybe they're feeling there's a big fight coming, they just don't know when, Link said. That's what I would have done.

At 1 a.m., the Marines start digging foxholes next to their humvees.

Earlier in the evening, when their convoy crept through the desert, the Marines had watched the tracks that crisscrossed the desert: humvee tire tracks; small tracks, from gerbils or mice; and larger ones, from foxes or stray dogs. The ones to watch out for were human tracks -- possible signs that someone had laid a roadside bomb in the fine, ankle-deep dust.

But where they finally made camp, the dirt was packed hard and strewn with small rocks, making the wasteland look like the surface of the moon.

Next to the passenger door of his humvee, Link drew a rectangular shape on the ground with the tip of his shovel, and forcefully stabbed the ground. The shovel went in less than one inch.

F -- ing not good, he muttered. He took off his Kevlar helmet and his body armor. This ground is hard as a f -- ing rock. There's no f -- ing way.

But he continued to dig, as did the troops around him. For several minutes, the air filled with the sound of metal scraping against rock.

At one point, Thomson stepped away from the 3-inch-deep hole he had managed to gouge in the ground, contemplating his work.

It's like digging a grave, he says. I'll lay in my little grave, I'll put my sleeping bag on top of me, and I'll be warm. I've found out that the deeper you dig, the warmer it gets.

Last time we were out, he continued, the first day, I dug like a champion. The second day, I didn't dig deep enough, and I was cold.

He paused, then smiled.

I talk about digging as though I'd been digging graves all my life, he said, shaking his head.

Soon, everyone except for the Marines pulling guard duty was lying in the foxholes they had managed to dig. It became so quiet that the ticking of Link's wristwatch filled the air.

Then there were steps.

A Marine carrying a backpack walked past Link's humvee, looking lost.

I'm just freaking -- oh yeah, he said, remembering something, and walked away.

Link stretched out in his foxhole and fell asleep. Two hours later, the muezzin's call for prayer once again filled the dark predawn air.

Wake up, wake up, prayer is better than sleep, the muezzin called in melodious Arabic.

The Marines' night in the desert was over.