Detailed and Jumpy
The narration switches back and forth nimbly between the characters' memories and the present day. The device of the trial is largely responsible for this fluidity; when characters testify during the present-day timeline, their testimony directs the narrative seamlessly back into the past. Once we're in the characters' memories, we actually get far more background and psychological detail than they are probably offering to the court.
Take, for example, Etta Heine. While she's testifying about the land dispute between her family and the Miyamotos, she takes us back to the day she and her husband got word of the enforced detention of San Piedro's Japanese and Japanese-American residents. While we're in her memories, we get some pretty personal details about her emotions and conflicts in their marriage, as well as the facts that were relevant to the trial:
"It's too bad," he said. "It ain't right."
"They're Japs," answered Etta. "We're in a war with them. We can't have spies around."
Carl shook his head and, heavy as he was, swiveled in his chair to face her.
"We ain't right together," he told Etta flatly. "You and me, we just ain't right."
She knew, indeed, what he meant by that. But just the same she didn't answer. Anyway, he had said this sort of thing before. It didn't hurt very much. (9.68-72)
We don't know how much of this story came out in Etta's actual testimony and how much just remained in her head, but the point is that Guterson's narrative goes beyond relying on character testimony to get the dirty details about the past; it actually takes you back in time and into the minds of the characters to get at their thought processes and emotions (as well as their recall of events).