I have overviewed studies of denosovian inter breeeding with modern humans that range from from 800,000 years ago to only 15,000 years ago in Papu New Guinea. Both are two seperate events and not continuous.
With mitochondrial DNA from large denosovian teeth it has shown populations in South Asian Indonesia show as much as 5% denosovian dna present especially in shared Gene 2. At any rate it doesn't matter much in this day and age, 'lawn chair paleoarcheologists agree'.
There does seem to be a mysterious relative or relatives with 46 chromosomes that started the human hominid branch in all its early diversity.

Dave btw in January I slipped and fell in Niagara Falls on the American side at Terrapin point. The exact spot was deemed too dangerous and was dynamited years ago. I was saved by my actual fingernails and two friends as I was only in up to my waist in slow current but the edge was only meters away. I remember how my pants were frozen solid on the walk back to the car.
People do inner tube in the fast Niagara river miles above Horseshoe Falls in July.