In the first picture we see snow on the north-facing rise to the south of the tracks. No surprise there. A question that might be asked is why the snow has melted on the other north-facing slopes.
In the second picture we see that there is still a small area of ice adjacent to the stream. You can see the sunlight and shadows playing on the ice, so this spot has not been entirely shaded during the winter and spring. This suggests that the remaining ice is on very low ground, where the cold air falls.
The next picture is of the stream, which typically is covered with ice during the winter. You can see remaining snow to the left, where it is both on low ground (remember cold air is heavier than warm air, and therefore goes to the low ground), partly shaded by evergreens, and on the north-facing side.