I want to propose to my girlfriend somewhere beautiful, any suggestions?
I will be there in July 1- 6.
I would like to mention I will be driving from Dallas to Denver anywhere in between that is cool too know.

Sapphire Point in Summit County.  It's the scenic overlook at the top of Swan Mountain Road, overlooking Lake Dillon and the Ten Mile and Gore Ranges.

Sapphire Point on Google Images

They do lots of weddings up there.

Chataqua Park in Boulder would be good

Red Rocks or Arrowhead golf course might be nice, too.  Google some pics.  Both are only 30 min from Denver.

That's a classic shot.  Chautauqua Park is amazing.

People get married there.  Graduation photos, etc.

You can say a lot of stuff about Boulder,  but the Boulder Mountain Park is one hell of a city park and my favorite playground.  There are scenic overlooks all over.  Royal Arch (gotta hike), Lost Gulch Overlook (on Flagstaff Mt. Rd.), etc.

In the picture are some of the flatiron formations (the big rock chunks).  Right to left, First Flatiron, Second Flatiron, Third (home of the Best Beginner Climb in the Solar System), Fourth, and Fifth.  The hiking trail that goes up between the First and Second is very popular.

I've made that drive (and reverse) plenty of times. Not much in between. If you're going through NM instead of Kansas, you could hit Garden of the Gods in CO Springs, although it gets somewhat crowded during the summer. Pikes Peak can look cool, but weather at the top can be unpredictable (not good for pictures). It can be hard to get good pictures at the Royal Gorge due to the flat colors. Most of the good stuff is a further west. Some areas around Crested Butte might be worth the drive.

I like this spot. I was also looking at Mount Evans scenic byway area.

Never climbed chautauqua.  Usually get a JLG.


If you're willing to add some miles, might look into a side-trip (might add a night somewhere, will add some time) to SW CO.  
Silverton, Ouray, Gunnison, CB, BV, Leadville.  Much prettier/scenic areas that way, not far off the highway.  And the highway itself is a much prettier drive than 25.  

Montrose~ish


and near Red Mountain Pass/Black Bear Pass, Ouray, off 550.  I think this is driveable (in a car), if not it's easily hikeable.


Vail Pass/Camp Hale.  I'm pretty sure this area's driveable (never been there in the summer), get to the Camp Hale monument, over the bridge and go right, then continue east for a mile or three


Silverton

What monument are you talking about?  The Camp Hale National Monument is not near Vail Pass but on the Eagle River between Minturn and Leadville.

That one.  
"Vail Pass" to me is that riding area, Ptarmigan Hill on the leadville side, ride the RR tracks over to Mango's for lunch, then back over the hill to the vail pass rest area.  
None of it's more than an hour by snowmobile.

Take this road over the bridge the last cat in the group's about to go over, then hang a right.


Mosquito Pass on the Leadville side

Gotcha.  Not the usual perspective.

Go to Estes Park and pick a place

This right here. I have a great picture of my family at Sapphire point. You  might have to wait in line to get your photo opportunity.

Red Rocks is also a good place.

Garden of the Gods in Colorado Springs.