Uluru to Coober Pedy

Just before you get to Marla , you could go in and have a look at Mintabie Opal Fields :)

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Could i hang a left at Cadney Park & head to Arckaringa (see painted desert) then to Mount Barry & down to C.P.what are the roads like?

I don't know how many times I've driven past the Mintabie turnoff and not gone in to have a squiz. It's a dirt road but could I tow a conventional van in or should I leave it at Marla?
Grunter, the roads you are talking about are dirt and quite corrugated. With a 4x4 and off road trailer you would have no worries.... fill up at Cadney though not much else available.

Well most people that go in leave their vans in Marla then go back and take the 33 k's trip out to the opal fields first to have a look , if they get hooked , they can always come back and get their van if they decide to stay for a few days . You are on Anangu Pitjantjatjara lands after you go over the grid about half way , so it pays to get a permit from the local police station in Marla first , to keep it legal :)

In regards to fuel cheaper to fill up at Kulgera or Erldunda rather than Cadney.

Just returned from that area last week and Cadney was about $1.62 (diesel) whilst Kulgera and Erldunda were cheaper (cannot remeber exact but less than $1.60).

If filling up at Coober Pedy there is a Opal Miners co-op fuel place in back streets (speak to accomodation places) and are apparently cheaper than those on the main strip.

We stayed at Riba's Caravan Park where there is underground camp sites (basically small gravel floor and could pitch tent or just have sleeping bag) and they told me about the Opal Miners Co-op after I had filled up. Riba's is on the William Creek round about 5 k out of town. They do a mine tour at about 7pm and if you do the tour then camp fee is $0. Ended up being $18 per adult, would be about $12 without the tour.

Cheers