I posted some of these photos earlier and have been trying to resolve questions about them, such as where they were taken and why my sister and I didn't appear. After looking through more of the scanned photo bonanza, I found more photos that are obviously connected! So things are starting to make a little more sense.
I still don't know where the rock formations are, but in addition to the already discovered photos of my mother and my father, now we have one with all three of us children.
The first photo in this next set we've seen before: my mother and my brother at a picnic table with the Toyota station wagon in the background. I found a second photo of a picnic table (possibly the same one?) with my mother and all three of us kids around it, obviously taken later in the day. My mother and my brother are wearing the same clothes as in the photos at the rock formations. It's harder to tell if my sister and I are wearing the same clothes, because we have jackets on, but Stacy's red shirt can be seen beneath her jacket, so my guess is yes.
And now we kids are inside a tent! This still seems to be the same day, because the clothes are mostly the same. In the second photo, the identifications are easy: Stacy, me, Mark. But in the first photo, I'm not positive who the girl is. She has a red shirt, which Stacy does in the first photo, but blue pants, which I do in the first photo. I believe it's Stacy, because she has blue pants in the rock formation photo. But I don't know why she changed pants between these two photos (or why I'm not in the first photo)!
I have previously posted the photo of my mother staring off into the distance with a lake in the background. The new one is my mother with my brother and me. We're wearing different clothes from the previous photos, so I'm guessing this is the next day. I vaguely remember that we had a camping vacation at Lake Mead once, so that's my best guess as to the lake. I welcome suggestions on how I can try to find images of Lake Mead from around April 1970 to compare to these.
Here's the Toyota again, with my mother and the three of us and a tent in the background. My mother, my brother, and I are wearing the same clothes as in the lake photos, so this should be that same day. At first I thought this might have been us getting up in the morning and the lake photos were later, but these are the only two photos that are dated May 70 instead of April 70, which would suggest they were developed later. So my hypothesis is these were on the next roll of film and therefore taken after the lake photos. I think this is the tent from the two interior photos above, but the tent is still up, so if these photos are later in the day than the lake photos, we don't seem to be leaving yet. The tent in the background of the evening photo looks different to be, so I don't think it's ours.
These are all the photos I have discovered so far that appear to be related. I think I've placed the photos in logical order, but I'm happy to hear comments on whether they should be arranged differently. This certainly has been an interesting exercise. And maybe I'll find more photos later to add to the sequence!