There's lots of great handmade singletrack in the Maraetai forest which is next door to the Whitford Forest. Both areas are looked after by the Pohutukawa Coast Bike Club. The forests are privately owned and a $10 day permit to enter is required if you're not a club member. The permit comes with a map which you'll probably need! Information about the individual tracks is listed on the club's website here: www.pcbc.co.nz/tracks/ Click on the individual trails for trailforks.com maps, profiles and latest conditions.
The trails are technical. Expect lots of berms, switchbacks, roots, off-camber curves, occasionally flow, lots of surprises. You won't find machine made table-top jumps or new-school flow trails. I didn't find any big drops but there are some very interesting concaves on the trail called Ground Effect. The trail called Native Addiction is "full of high speed runs through native trees into swooping hip jumps and amazing drop berms".
The terrain is not rocky - its clay which can get very slippery when wet. The trails tend to get a bit rutted over winter. Generally you climb up forestry roads then shred down singletrack. Lots of the trails are in recently planted plantation forest, some are in more mature pine forest, a few are in regenerating native forest.
Maraetai Forest is not for the faint-hearted or beginner - you need at least intermediate skills to enjoy it - and a good level of fitness!