Some areas topped 100 degrees, particularly in the inland and high desert communities.
Workout enthusiasts wanting to avoid hot conditions were at the Rose Bowl in Pasadena early in the morning. Highs in the city were slated for 98.
"We see people around the Rose Bowl working out early in the morning, which is great," said Pasadena Fire spokeswoman Lisa Derderian. Pasadena Fire says it responds to more medical calls when the mercury rises.
"If you plan on working out later in the evening when it cools off, start hydrating yourself earlier in the day," Derderian said. "If you wait until you're thirsty to drink, it's more than likely too late. That leads to heat cramps, heat stroke, heat exhaustion."
Pasadena Fire also reminds people to check on any elderly neighbors or friends who may not have or use air conditioning. Anyone who feels faint, disoriented or has a headache should seek medical attention.
With temps soaring well past the 100 degree mark, the Inland Empire continued to sizzle under an extreme heat advisory.
As temps rise, so do the number of emergency room visits for heat-related illnesses.
"We're starting to see some of that ... the increase in visits, a day or two after the arrival of high temperatures," said Dr. James Suel of JFK Memorial Hospital in Indio.
In Lancaster, the city's Museum of Art and History is doubling as a cooling center. It's open to anyone who wants to cool off from the triple digit heat and enjoy the exhibits.
Cooling center locations have also been established throughout L.A. and San Bernardino counties. You can see a list of locations or dial 211 to find a cooling center near you.
Authorities want to remind people that children and pets should not be left unattended in cars with the windows up.