Gary also sent in this link – www.dailymail.co.uk/sciencetech/article-10069819/ … Mars Jezero crater was a lake – estimated 3.7 billion years ago. Until a flash flood deposited large boulders on to the delta – according to evidence from NASAs Perseverance Rover. The rover vehicle has been trundling along the bottom of the crater, taking samples, since February. It has also taken a lot of images that have subsequently been beamed back to earth. Something, deep in the past, caused boulders from miles away to be dumped inside the crater. A flash flood has been suggested – and quickly accepted.
When seen from above the crater resembled river deltas on earth, where layers of sediment are deposited in the shape of a fan. In this case, the fan is where a river once fed into the lake. Images taken inside the crater seem to show the outcrops were a river delta – but a dramatic shift in climate [?] triggered episodic flooding towards the end of the lake's existence. Now it is a dry desert like environment.
See also https://phys.org/news/2021-10-rover-images-jezero-crater-ancient.html … and published in the journal Science – https://doi.org/10.1126/science.abl4051 … or https://www.science.org/doi/10.1126/science.abl4051 …
and see also https://phys.org/news/2021-10-floor-jezero-crater-mars-sustained.html … rocks on the floor of the Jezero crater on Mars show signs of sustained interaction with water. The lake system and rivers that drained into the crater were 'likely' between 3.8 and 3.6 billion years ago – but the rocks are yet to be directly dated in an earth laboratory. See also https://gsa.confex.com/gsa/2021AM/meetingapp.cgi/Paper/367543
William sent in a link with the comment. Donal W Patten thought an icy moon may have broked up over Mars producing a watery deluge. He then provides another link to the story – https://www.yahoo.com/news/perseverance-rover-finds-evidence-ancient-170… … with the evidence of a flash flood, and https://www.yahoo.com/news/nasas-perseverance-rover-mars-rover-found-180… … which repeats the find of the boulders and the implications.