Note: This story is a prequel to my Buffy/Stargate crossover: Misunderstandings
Too Good to be True
Chapter 1:

Colonel Jack O'Neill squinted against the harsh sunlight. He pulled his sunglasses out of a breast pocket of his BDU, flipped them open and slipped them over his eyes. He heard the wormhole collapse in the stargate behind him as he looked around. SG-1 had just emerged from a gate at the head of a mountain valley. It might have been a valley somewhere in Washington State, or maybe southern British Columbia, but the blue of the sky wasn't quite right, and the colour of the vegetation was a little off. He bounced up and down on the balls of his feet, enjoying the feel of a gravity field only about 4/5ths as strong as Earth's. He was sure that his knees would appreciate it.

P3G-823 looked like any one of dozens of other worlds that SG-1 had been to. Mountains, trees, temperate climate. Nearly all the indicators said that this was an ideal world. The sort of place where Jack would like to have a cabin, beside a nice stream with lots of fish in it. He had long ago decided any place that seemed as nice as this, was just too good to be true.

The first MALP had been sent here over a year ago, and it hadn't discovered anything out of the ordinary. No signs of any civilization, or current habitation of any sort.

That was the main thing that this world seemed to have going for it: it was empty. No natives to worry about offending, no Goa'uld, nothing, and that was unusual. Gates weren't usually left on worlds that had no reason for people to visit them.

A couple of months had passed before any more exploration was done. A UAV had been sent through the gate, to scout farther than the very short range that the MALP could reach. It had found the remains of a road, leading away from the gate. Sections of it had been buried by landslides, and much of it was overgrown by trees. Their roots, and a thousand years of weathering had nearly obliterated the parts that weren't buried.

The UAV had followed the road to some ruins, a few kilometres downhill from the gate—the tumbled down remains of what had once been a large stone structure—so this world had obviously been inhabited at some time in the distant past, but there was no sign of what may have become of those inhabitants.

Still, there really hadn't been any reason to send anyone to this world to explore it more thoroughly. There were lots of more interesting worlds on which the SGC could spend its limited resources. More months had gone by during which no one had come here.

But eventually they had sent someone. SG-12 had come through the gate two weeks ago, to do a scientific survey of the planet. For twelve days they had sent back regular, boring, reports. Daniel had been excited by the pictures of inscriptions from the ruins that the archaeologists had sent back, but he was the only one. The geologists hadn't found any minerals worth mining; the botanists, and zoologists hadn't found any useful looking plants or animals.

Daniel had been grousing for a week about not being allowed to go see the ruins for himself, but he'd been tied up trying to gather as much information as he could about this new Goa'uld, Anubis. General Hammond had thought that that was more important than a thousand year old ruin. The ruin wasn't going anywhere.

Then, twenty-four hours ago, SG-12 had missed their scheduled check-in. The SGC had dialled out, and tried to raise them, but they had received no response to their radio call. Another UAV had been sent. It had overflown their campsite, near the ruin, and it had shown no one: just the tents, and some equipment, no sign of SG-12, and no sign of any sort of attack. Under infrared, the UAV could see the warmth from some equipment that had been left running, but there was no sign of any body heat that might come from someone sheltering in one of the tents, or hiding in the trees.

So now, here they were. SG-1 was standing in front of a stargate on a world that had seemed too good to be true, and now it looked like Jack's suspicions were confirmed. He took one more look around the peaceful valley, before he waved his hand in the direction of ruin. "Let's get moving campers. We don't have all day."