Some excellent posts OtherHand and BretPCT, thanks for adding further pieces of info.
As I mentioned in previous post, the (only) likely reason they would go back uphill into the second wash is because they'd seen houses below, tried to make a phone call out, failed, and then went up the second wash with the idea that they might get coverage if they just got a little higher above ground.
The blood spot, if it was legitimate, could suggest an injury received while boulder-scrambling or climbing. This could have initiated panic, perhaps worsened by drug use (I've found MANY posts online in which people talk about scrambling boulders at JTNP while ON drugs.) Maybe, after not getting cell response near the site of the accident, Orbeso foolishly decided that the fastest way to get Nguyen to help would be to go down the wash, rather than returning on the trail.
Or. The blood spot (if it was legitimate) could support Wildhorse's notion of a forced-march kidnapping, in which Nguyen and Orbeso argued violently and physically during the hike--resulting in an injury to Nguyen--and Orbeso forced Nguyen to walk down the wash. When Orbeso saw houses below, he forced Nguyen up a smaller side canyon to the area where he made the decision to kill her. A lurid and extreme explanation, certainly--but this event DID end in a murder-suicide, after all.
It seems to me the key to find the truth here will really be whether their phones show evidence of attempted 911 calls.