SANTA CLARA, Calif. -- The ominous skies hovering over Levi's Stadium haven't yet forced the San Francisco 49ers to change their plans, but it's something they and the NFL will have to keep tabs on as they head toward Sunday's opener against the Arizona Cardinals.

With more wildfires burning all over California combined with a recent heat wave, Bay Area residents woke up to eerie orange skies and falling ash on Wednesday. It created a strange atmosphere for the Niners and coach Kyle Shanahan as they conducted a walk-through and a practice outside the SAP training facility.

"We just got back in from walk-through and it's orange out here, too," Shanahan said. "I feel like I'm in 'The Book of Eli' -- it's like an apocalyptic state out there."

Despite the dark pall over their practice fields, the air quality, at least for now, has not surged into dangerous territory. According to Shanahan, the team's measurement on the air quality index was a healthy 69 during the team's walk-through Wednesday. That number remained in the 60s during practice.

That's notable because the NFL will not allow teams to play or practice outside should that number surge to 200 or above on Sunday. To this point, the wildfires that have been burning for the past three weeks have not caused the Niners to cancel practice because of air quality.

On Aug. 21, the team did alter its practice schedule by about an hour because of concerns that winds would shift and the air quality would reach the threshold to force the Niners to cancel or move practice. The team also excused two players from practice early as a safeguard against the effects of the climbing air quality index number.

At that time, the air quality hovered between 150 and 155, and it has reached as high as the 160s at various points over the past few weeks.

"Surprisingly, the air quality doesn't seem as bad as it looks," Shanahan said. "A few weeks ago when we had it or last week, it got up, it got past 150 here for us. But today when we were just out there 15 minutes ago, that air quality was at 69, I think, which isn't close to what it's been. It definitely looked different out there."

While many of the fires from that time are close to full containment, new fires have sparked in recent days. According to the California Department of Forestry and Fire Protection, wildfires have burned over 2.5 million acres in the state this year, with eight deaths and more than 3,700 structures destroyed as of Wednesday morning.

Although none of the fires are in the immediate proximity of Levi's Stadium, high winds have blown smoke and ash over all parts of the Bay Area, including the 49ers' facility. Strange as it was, the Niners were able to practice Wednesday without problems.

"It's dark out there," quarterback Jimmy Garoppolo said. "It's not clouds. I mean, just with the smoke and everything, we just did a walk-through a little while ago and there's the ash falling all over the place. It's different, but [I] send best wishes to all the families out there that are dealing with it. It's tough times, and stay safe."

On the field, the 49ers were without wide receivers Deebo Samuel (foot) and Brandon Aiyuk (hamstring) and cornerback Jason Verrett (hamstring) for Wednesday's practice. Center Ben Garland, who has been dealing with an ankle injury, practiced on a limited basis.