Can you explain what the zone is in Roadside Picnic? Give an example from the reading using specific details.

The Zone is an alien landing site. The citizens of Earth wake up one day to learn that aliens have temporarily stopped by on Earth and have left several spots of close contact, which get named “Zones.” These zones correspond to ships landing at random on a spinning globe when launched from a great distance.
The Zone has many interesting properties and is filled with exotic matter, unique forms of radiation, and groundbreaking technology that was discarded by the aliens upon their departure. The event is likened to a group of people in their car stopping off at the side of the road for a picnic, perhaps changing and discarding a spark plug and leaving some used oil on the ground. The aliens are so far above us, they don’t even think to make contact, and they fail to consider the societal and ecological impact of the items left in the Zone.

Roadside Picnic is a 1971 Russian science fiction novel written by Arkady and Boris Strugatsky and translated to English by Antonina W. Bouis. It tells the story of the effects of the "Visitation," an event during which extraterrestrial visitors spent two days in six different spots around the earth. The title refers to a metaphor used within the story to describe the alien activity in relation to humanity; extraterrestrials briefly paused on Earth for a "roadside picnic," leaving behind their garbage and other materials much as humans might abandon their own clutter along the side of the road. 
There are six "Zones" throughout the Earth, each corresponding to one of the extraterrestrial landing sites. More properly termed Visitation Zones, each Zone is the site of strange artifacts and inexplicable phenomenon, which scientists, governments, and amateur hunters explore and attempt to understand. The importance of these Zones is described in the novel's introductory interview with the character Dr. Pilman:

After all, many very important scientists have proposed that the discoveries made in the Visitation Zones are capable of changing the entire course of our history.

Zones are often explored by groups of people called "stalkers," who dangerously and illegally enter them to essentially hunt for alien artifacts. The stalkers and their activities form the basis for the plot of the novel. 
Within the course of the story, the Zone specifically focused on is in Harmont, Canada. The stalker Red Schuhart makes a series of expeditions into this Zone over an eight-year period. It is full of objects that seem to defy all logic, including hazardous materials, legendary objects that can grant wishes, and others whose purposes are not known.