The two teams are also scheduled for a Sept. 1-3 series in Oakland.
Friday night's postponement was the Mariners' first rainout since May 15, 2011 at Cleveland. The last time Seattle was rained out in Oakland was April 10, 1982.
Mariners manager Lloyd McClendon said the mushy infield, created when a heavy rain fell Thursday night in Oakland after the A's grounds crew didn't put a tarp over the infield, was one of the worst field conditions he'd ever seen.
"I've never had a game canceled for that particular reason," McClendon said Saturday. "I almost turned my ankle [walking across the infield]. It was that bad. It was just not safe."
The makeup situation in such a postponement is up to the players union. Furbush said the A's initially wanted to play a doubleheader on Saturday, but they quickly agreed to delay it until a later date after the Mariners pushed for that idea.
"It was kind of interesting talking to everyone, trying to figure out what the best game plan was," Furbush said. "I was just trying to represent everyone as best as I could. Once we realized, given the playing conditions, that playing one [Saturday] was going to be better for us and wait until we come back to play two, that was the general consensus and that's the way it worked out."
Furbush said players' safety was the foremost concern.
"Part of it was just the playing conditions," Furbush said. "Lloyd went out there and almost twisted his ankle. It was pretty bad. You don't want anybody going out there getting hurt. I think the outfield was OK, but the infield, where a lot of hard cuts are being made, that's going to put the safety of everyone in question. So I think it worked out good."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.