More than $5,000 in prizes are up for grabs in the hats contest, which is free to enter and begins at 11:30 a.m. at the Plaza de Mexico. Judging will take place in the categories of Most Glamorous, Best Racing Theme, Funniest/Most Outrageous, Best Fascinator and Flowers/All Others.
The grand prize winner will receive a Harrah's Resort Southern California Luxury Resort Escape with two-night stay in a hotel suite, $200 meal credit and $200 spa credit.
Category winners will get $300 and $100 Studio Savvy gift certificate. The second place prize is $200 and third place $100.
The 40-day racing season will feature a new dirt track that replaces a synthetic surface that was in place for eight years.
According to the Del Mar Thoroughbred Club, about 31,000 tons of dirt known as El Segundo sand -- drawn from the El Segundo area near Los Angeles International Airport -- was placed on the one-mile oval. The same material is also used at Santa Anita.
The dirt track will also require less water than the former surface, according to the DMTC.
The dirt oval has already been tested by Triple Crown winner American Pharoah. The champion horse is working out at Del Mar in preparation for an Aug. 2 run at Monmouth Park in New Jersey, but is not expected to race locally.
As usual, the highlight of the Del Mar season will be the $1 million TVG Pacific Classic -- scheduled for Sunday, Aug. 22. The day will also include the $250,000 Pat O'Brien Stakes and $250,000 Del Mar Handicap.
The Opening Day featured race is the $100,000 Oceanside Stakes for 3- year-old's, which will be run on the one-mile turf track.
The racetrack's summer concert series is scheduled to begin Friday, with the Wallflowers. Eleven concerts are planned during the racing season on Fridays and Saturdays.
Opening Day admission is $10 for the Stretch Run and $20 for the clubhouse -- above the usual $6 and $10, respectively. Reserved seating will cost $25 on Opening Day.
Starting around 11 a.m., opening day traffic is expected to cause delays along Interstate 5 in both directions near Via de la Valle, according to Caltrans.
For patrons who want to take public transportation, the North County Transit District's Coaster train will stop at the Solana Beach station. Passengers may board shuttle buses for the ride to the racetrack.
Because of the large crowds that are expected, passengers are encouraged to purchase tickets in advance, either online or on smartphones.
The NCTD's promotional "Pony Express'' tickets are not valid on Opening Day.
Amtrak will also stop at Solana Beach during the racing season, which runs Wednesdays through Sundays until Sept. 7.