IN YELLOW we see what looks like Plasma Rifle markings in the stone. Perhaps Chief was hunted down or ambushed by the group that kidnapped Halsey? If it were Agent Locke who shot him down, you wouldn't see the glow around the markings.
The glow also leads me to believe it is a fairly recent attack that perhaps Locke finished up in rescuing chief. Plasma glow markings eventually fade away leaving burn marks... you can see here that there are still white or light blue markings around those markings which leads to believe it is a recent event. It also appears that Locke is placing a weapon back in it's holster, rather than pulling it out.
Perhaps he found chief being overwhelmed by covenant scavengers, chief collapses, Locke fights the baddies off damaging his helmet in the process.... leading him to remove his helmet after the fight is finished. He then approaches chiefs unconscious body carefully. The citizens come out of their homes and attempt to thank those that helped them etc. You get the idea... anyways...
IN PINK we see some strange markings that you see no where else on the map... what could they be? Confetti from dead grunts? nah.... perhaps they are just pieces of debris in the air that are floating around? Maybe they are attached to the monument?
IN ORANGE we see a strange man without any armor or anything special on. He has a hat... perhaps a farmer? When was the last place we saw a civilian in a Halo game? Halo Reach! #Reach2015
Also, on the left side of the structure, behind it... it appears there is a sign, is it a sign? If so... what could it be for and what could it say? Another hint?
IN GREEN we see some strange debris... one looks like a reservoir or piece of a military vehicle of some sort and another a very strong cable that looks like it has been easily snapped. What could this lead to? There was some sort of wreckage or material break down here... really we just need to know what it was.
That just about sums up some of the things I noticed... I am pretty sure it is Reach, as Twinreapers points are very strong and everything in the image lines up.
EDIT: Also, look at the black ash up-splash on the monument, looks like a bomb or grenade detonated close by.