Was the ground really "much too rocky" for R2?

Question

In A New Hope, C-3PO says to R2-D2:

Where do you think you're going?
Well, I'm not going that way.
It's much too rocky.
^{_{- A New Hope script}}

Later we see the place where R2 has wandered, and I've always thought to myself that C-3PO was right; that place looks much too rocky for R2 to drive around. In fact, it even looks like they had to smooth out the ground just so R2's wheels could roll properly.

Behold the suspiciously smooth ground that is surrounded by rough gravel:

TL;DR: Did the filmmakers have to smooth out the ground to allow R2 to roll around? Or was this smooth section a happy coincidence?

Answer 1

In-Universe:

From the original script¹:

           Suddenly Artoo whistles, makes a sharp right turn and starts 
           off in the direction of the rocky desert mesas. Threepio 
           stops and yells at him.

                                 THREEPIO
                     Where are you going?

           A stream of electronic noises pours forth from the small 
           robot.

                                 THREEPIO
                     Well, I'm not going that way. It's 
                     much too rocky. This way is much 
                     easier.

           Artoo counters with a long whistle.

                                 THREEPIO
                     What makes you think there are 
                     settlements over there?

           Artoo continues to make beeping sounds.

You can see from C-3PO's next line that he his intent on looking for civilization. He is more keen on doing so by walking over the soft slopes of the dunes rather than attempting to scale shuffle-up a rock face to get there.

Out-of-Universe:

These scenes where shot in Sidi Bouhlel². Looking at the canyon where these scenes where shot (here) there appears to be several areas of flattened/hardened land for the crew to drive their RC robot across.

Seeing as these flattened areas are still present in more modern photography (also here), I think that it is safe to assume that these areas that R2-D2 is seen on were natural occurrences that were selected for the shoot.

I also doubt that they would have attempted to alter the desert landscape instead of just cheating a bit when they really needed to get R2-D2 rolling³.