Your current order is incorrect and needs to be adjusted for proper functionality.
Here is the revised code:
The HTML:
<div class="large-image-container"> </div>
<div class="content-col-text"> </div>
<div class="gallery-thumb-container"> </div>
The CSS:
.large-image-container{float:left; width:66%; background:red;}
.gallery-thumb-container{float:left; width:66%; background:yellow;}
.content-col-text{float:right; width:31%; background:green;}
Check out the Demo on Fiddle:
DEMO
In most cases, adding clear:both;
can help correct float issues and ensure smooth operation.
I hope this information proves useful in resolving your concerns.