It looks a bit more like Blechnum nudum from the photographs. Check the base of the stipes (fronds). If there are black scales, that suggests B. cartilagineum, otherwise B. nudum. On e very distinctive feature of B. cartilagineum is that the pinnae at the base of the frond are quite long, and tend to point backward, away from the frond tip. B. nudum has much shorter initial pinnae and the are all more or less perpendicular to the stipe (stalk).
I can't get really close to the fern as it is halfway up a bit of eroded creek bank with the creek running below it. I thought it could be B. cartilagineum as the fronds seemed quite wide at the base
I suspect it's B. nudum, but it would be useful to confirm the scales, and the presence (or otherwise) of long rear-ward pointing pinnae at the base of the frond. It's an interesting find in such an open location, regardless of species.
I managed to scramble over to the fern as the creek had dried up and photographed the stems. They were all dark reddish brown (see latest photo). I presume this means that it was definitely B. nudum, not B. cartilagineum.