A 5.8 can be considered a major earthquake, but its only poor designed or built structures that have problems with something under 6 in California's earthquake areas usually. The '87 Whittier quake (5.9 richter) killed a child who was buried by a brick wall that wasn't built to code, and a student at LA City College who was crushed by a big slab of concrete that fell off the parking garage she was near.
My first info came from local news reports, but the Desert Dispatch has an AP report "Strong quake shakes Southern California" up on that now.
Excerpt:
Preliminary information from the U.S. Geological Survey estimated the quake at magnitude 5.8, centered 29 miles east-southeast of downtown Los Angeles near Chino Hills in San Bernardino County.
Read rest at source includes link to map of area.
Within a half hour the Chino Hills earthquake was downgraded to 5.4, but unfortunately I was off and busy.
Reading the news tonight I found that most of what I surmized was true, that all the retrofitting since the 87 Whittier and the 94 Northridge quake had ensured there was little damage to structures or infrastructure. The kinds of 7 richter scale quake we've had in the desert areas (on or near the famous San Andreas fault -- the one that's suppose to drop half of CA into the sea some day according to popular lore with no real scientific backing) could have caused real problems, still one report noted that most of Chino Hills area had been built since Northridge quake and the code calls for safety up to richter 8. Yet, things do fall in the desert quakes.
A good report on the tremblor is the LA Times: Minor damage from 5.4 quake shows California has learned its lessons.