A few pieces of advice re Magic Mountain since I live about 1 hour from there.If you're going in June expect it to be hot. I mean upper 90s type heat. You may luck out and have nice weather but be prepared for the heat.Expect less than stellar customer service. The last few times we went to MM it seemed like everybody that worked there wanted to be somewhere else. Obviously food and drinks inside the park are going to be expensive. It's not as bad as Disneyland but it's no joke. Of course if you're going without kids it won't be as big of a deal.Whatever you do when you leave the park do NOT head north on I-5. You might end up in Bakersfield.
I'm going to disagree on the heat. It's typically only moderately warm in June, and often can be overcast, i.e. "June gloom", but we didn't get much of that last year. Usually July through mid-Sept is the hottest time. Still, summer dress is appropriate but bring extra layers, e.g. a sweater, light jacket, sweatshirt, etc. to throw on, especially if you're within 5-10 miles of the ocean. The fog can roll in and the temp can rapidly drop 10-20 degrees.
THIS. Biggest misconception about So Cal is people think of June as a hot month, and more times than not the June gloom will keep even inland areas like Valencia where Magic Mountain is cool/comfortable. Just know that visiting the beaches in June will often mean bringing a sweater. Again, it's luck of the draw, but it really is the rule rather than the exception. July-October are a lot more predictably sunny. January for that matter.Lots of good suggestions here. I'd just group days. You could do the Getty Museum, 3rd street promenade in Santa Monica, and the drive up PCH in Malibu. Stop at a joint like The Reel Inn to get some local flavor. Fresh fish, good beer, overlooking the beach, what's not to like? Go for Magic Mountain if you like coasters. No other park in So Cal comes close. Don't worry, it's safe. If you're into that music I'd recommend doing the Whiskey, Roxy, etc. Lots of history there. Personally, I avoid Hollywood Blvd but there are some very cool shops and restaurants on Melrose. Good comedy at the Improv. Combining the Echo Park scene with a Dodger game is very cool. Definitely do the Hollywood Bowl if you get a chance. Go somewhere and have them make you a great basket lunch, bring some wine, and hang out at the benches in the grassy areas before the entrance. The Greek Theatre has great acoustics as well. So much to do - just know your destination and plan your drive time. 10X better to drive down to Echo Park at 3 or so to hang out before a Dodger game then drive the madness at 5pm.LA Live/Nokia/Staples Center is cool too. LA Theatre is not bad at venues like the Pantages, etc.Have fun!