This begins as a paved path along the Santa Ana River. It is not very scenic due to a huge wall separating you from the river. About a third of the way through, you'll hit dirt and it opens up wonderfully!
There are a lot of baby-head rocks on this portion of the trail. There will possibly be a stream crossing if the river is flowing high. After that, you are on more of a dirt road surface which is very hard packed, but very rocky.