Those times are very very good.
Arcadia's mark at the state meet in 2010 is just a little better than GO's Mt. Sac Course Record and that team may be the best high school team ever. I project Great Oaks time to be somewhere in the 76:30 range for Woodward park. Here is a link to compare that team to previous CA and other teams from the past including Mead HS from 1993.
http://www.prepcaltrack.com/all-time-california-cross-country-lists/
So not knowing too much about the competition around the country I would say Great Oak has a really good chance to win Nike Nationals this year, especially because of their 1-2-3 punch which may score them 10-15 points total.
Dana Hills is a notch behind Great Oak right now for sure, but they tend to do better at the years end so I would guess they are close to a 77:00 team at Woodward, which means they are also in contention for a podium finish (since Arcadia 2012 won NXN with that team time).
All in all, both teams are significantly better than last year's CA represented and it would be shocking if both weren't in the top 5.