Outback 3 West MacDonnell Ranges: Simpsons Gap

The eastern end of the West MacDonnell Ranges were looking pretty good as we approached Simpsons Gap (see map below). Before going into the Gap we walked up nearby Cassia Hill, from where there were even better views.

Silver Cassia in the foreground

Simpsons Gap from Cassia Hill

Cassia Hill walk is just short of 2 km in length and takes about an hour, they say, but in reality can be done much quicker. There's a self-guide sheet available so you can spot the low-growing shrubs that give the Hill its name, as well as Fuchsias, Desert Bloodwood and the ubiquitous Mulga. You'll also see Buffel Grass signed which is certainly not native and, although loved by graziers, is loathed by those trying to rid conservation areas of exotic invaders. It was introduced to the Northern Territory in the 1950s in an attempt to control erosion, but it is an aggressive coloniser that intensifies fires and then grows back all the better for them. Native grass species can't compete.

Cassia also known as Senna

Desert Bloodwood

As in most ecosystems, the plants that grow in particular parts of these Ranges are determined by moisture content, soil type and whether it is sunny or shady. On north-facing scree slopes where shallow dry soils are exposed to hot sun, Spinifex thrives. Hilly areas with greater surface run-off support thicker vegetation, and here Mulga dominates. Near creeks and on alluvial flood plains, Ghost Gums grow tall where soil is deep and moist, but are stunted if soils are thin and dry. On shadier slopes, Cycads survive if their roots can reach water via rock crevices; and Native Fig and Native Fuchsia occur lower down. Few plants flourish on exposed ridge tops except Native Pines.

Mulga trees may look thin and weedy, but the wood is robust and durable and has long been used for tools and weapons. Traditionally, the seeds are roasted and ground into the Aboriginal version of peanut butter. Mulga is widespread and an opportunist: it flowers when it can, that is, when moisture is available, so seeds may be produced even in essentially dry periods.

At Simpsons Gap we were still in Heavitree Quartzite country, with the now familiar story of sediments laid down in the Amadeus Basin being uplifted and/or contorted into different formations that have since been eroded. Roe Creek cut the Gap in the Quartzite when the whole landscape was higher than it is now, having been pushed up into a great anticline. Most of it has since been eroded, and Cassia Hill is a remnant of a Schist basement rock that underlaid the Amadeus Basin sediments. That makes it about 1600 million years old, one of Australia's oldest rock formations.

Today there is a permanent waterhole in Simpsons Gap surrounded by dramatic rock walls. It was late in the day by the time we got there. There was no sun to highlight the red rock, but the still air made for some great reflections.

As I look at my photographs weeks later, I can't work out exactly what is what in some of them.

Another pic that's hard to read is this one.

This rocky hotchpotch sloped upwards, and this is where Black-footed Rock-wallabies might hang at certain times of day. They are mainly active at night, but in the morning or late afternoon they forage in nearby shrubs and grasses. If the sun is hot, they'll stay behind shady rocks, but they may be tempted to bask awhile in kinder winter sunshine. 

In the 1930s, large groups of these animals were observed, but by the 60s they were far fewer in number. Their decline has continued, to the extent that they are now classed as Threatened, largely due to predation by some introduced species and habitat change by others. The West MacDonnell National Park is vitally important to their survival. There are believed to be about 20 living at Simpsons Gap.

We sat quietly and scanned the rocks for some time, hoping everyone else would leave before we had to, or at least keep quiet. Wallabies are sure-footed and agile, thanks to rough pads on their feet and a substantial tail to assist with balance, so it's best to watch for movement. They are well camouflaged, however, so the eyes of a hawk are useful. We eventually spotted a couple, although they were quite high up the slope and not easy to make out. Then the dilemma: do you just enjoy the moment or try to grab a photo? Fortunately, my friend managed to get this. The one just below the large rock on the right seems to have a joey in the pouch; her mate has his back to us, half way along the top of the big rock (click on pic to make it bigger).

One thing that has always impressed me about Wallabies is the female's reproductive abilities. Environmental conditions obviously have to be conducive to reproduction, but once they are, the female Wallaby is highly efficient. She can have a joey 'at heel', another in her pouch (where they spend up to six months), and a fertilised egg in her uterus, ready to go. She can produce two different types of milk, according to demand. Extraordinary. 

I almost forgot… As we sat on a rock waiting and hoping for Wallaby action, this delightful little Dusky Grasswren darted past our feet. 

It was nearly 6.30 and we had to get on into The Alice. On the way back to the car I noticed this sign. After my thoughts at Ellery Big Hole, it made me smile. 

This post was last updated on 1 October 2015