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LAS VEGAS — The San Francisco 49ers landed in Las Vegas on Sunday, and they're trying to get their footing ahead of Super Bowl LVIII.

Sources tell CBS Sports some 49ers staffers are not pleased with the practice field at UNLV, where the NFL designated the NFC champion practice during Super Bowl week. At issue, sources say, is the firmness of the natural grass the NFL has laid over UNLV's artificial turf ahead of the 49ers practicing there.

A 49ers advance group that includes members of the equipment staff and grounds team traveled to Las Vegas last week to check out the facilities. They feel the grass is too soft for the team to practice on, and the team has considered alternatives, sources say. 

49ers players and coaches had not yet visited the field, having just arrived in Las Vegas Sunday around 6:30 p.m. local time. They are scheduled for a walkthrough there Monday afternoon. 

Sources say this is not a health-and-safety issue as much as it's simply a preference issue. Sources say the current surface at UNLV meets all NFL, NFL Players Association and independent standards.

Among the tools the league uses to make sure a field is up to code is the "Clegg" test, which measures a field's firmness. NFL fields have to be at or below 100g (units of gravity) to pass. According to a source, the natural grass at UNLV measures around 50g, whereas the 49ers have a preference around 70g.

The 49ers have three options as it stands Monday ahead of their walkthrough. They can a) go about their business and practice on the field as scheduled; b) bring in new, firmer sod that would, in theory, be ready for practice this week; or c) negotiate with the NFL to practice at the Las Vegas Raiders practice facility where the Chiefs are located this week.

Sources say there have been discussions about the 49ers adjusting their schedule that would allow for them to practice at the Raiders' facilities when the Chiefs aren't there. But sources also indicated that, before the 49ers ever step on the field, the likely scenario is that San Francisco remains at UNLV.

Each year at the Super Bowl the NFL designates one team as the home team and the other as the away team. That alternates each year, and this year the AFC champion is considered the home team. Usually that means the home team gets to practice at the local NFL team's facilities while the away team practices at the best college facilities nearby.

Last year, the Chiefs were the away team and practiced at Arizona State, while the Eagles were at the Cardinals' facilities.

The debate over playing surfaces has been a polarizing topic in the NFL for years — especially this past season.

While the Raiders' new complex has both artificial and natural grass fields, UNLV's Fertitta Football Complex only has artificial turf. Though the NFL, through joint studies with the NFL Players Association, show little difference between injury rates on natural grass and artificial surfaces, players regularly complain about how their bodies feel after practicing or playing on artificial surfaces.

The NFL had an issue with its Super Bowl LVII field last year. Both the Chiefs and Eagles struggled with footing on the slippery surface inside State Farm Stadium. Philadelphia's league-leading pass rush didn't sack Patrick Mahomes once in the game.

Afterward, longtime NFL groundskeeper George Toma said that field had too much water and not enough sunlight in the leadup to the game.

Allegiant Stadium has a tray system similar to Arizona's last year. The league is aware of the criticisms and addressed any concerns in a conference call last month.

"We have brought in a brand-new natural grass surface that is currently installed in the field tray outside Allegiant Stadium," NFL EVP Peter O'Reilly said recently. "That has been in for a little bit now and is working through all our standard testing procedures that will take place over the time from installation up through the day before and that Saturday right before the game. Those adjustments and a core maintenance program are in place so we have an optimal field on game day."