Someone on a local games day list asked why rent in South Boulder is so expensive and why the roads are so wide and the yards so big. Cribbing from Boulder History Museum's timeline
and 35 years of stories from my dad and others, here's some background.
Boulder's population more than trebled from 1950 to 1970, driven in part by easier access, good science/engineering jobs, and post-war suburban boom that visited most of the country. Martin Acres was the first large-scale cookie-cutter housing development in Boulder, with a lot of cheap modest houses.
Development of the Table Mesa subdivision (which includes Emerson) occurred in the mid-60s at the base of the fancy new NCAR. With several other high-tech employers in the south part of town and a booming economy, the Table Mesa neighborhood targeted well-paid professionals with families, leading to the ubiquitous 2-level with a two car garage, a porch, and a big yard.
While the Blue Line
policy restricting housing development on the mountain sides was introduced in 1959 and the city started buying open space in 1967, most of Boulder's growth-restrictive policies didn't start until the 1970s. By then Boulder was one of the national centers of environmentalist culture and had begun attracting recreational and outdoor enthusiasts. In addition to environmental concerns, growth restrictions play to the advantage of existing homeowners (who are also, not coincidentally, the primary electorate). By preserving open space and limiting housing construction, market value for existing houses goes up on account of demand outpacing supply and the house having a nice view and convenient outdoor recreation.
Boulder has continued limited growth policies for the last 40 years, but has only really been concerned about soaring housing prices for the last 20 or so and they've only gotten serious about density in perhaps the last 15 years. These days there seems to be wide support for dense (but not tall) housing and New Urbanism ideas like mixed use development. Yet with a greenbelt of permanent open space, transitioning to this model is slow. There aren't many places one could build a new subdivision on these principles. And even single family houses which get bought and torn down usually get replaced by a much larger, fancier single family house rather than a multi-family dwelling.
So why are rents in Boulder so high? Demand greatly exceeds supply and there are social limits to increasing supply. Why is demand so high, even at high prices? Boulder's one of the most enjoyable places in the country to live for certain sets of people, including professionals (who can often afford Boulder housing prices) and students (who can include rent in their student loans). And part of the reason that Boulder is an attractive place to live are the restrictions on growth. The construction-focused policies of Denver's suburbs has resulted in a lot of houses which are pleasant as dwellings but hasn't led to any communities as attractive as Boulder, let alone Boulder's geographic perks.
 My grandfather told my dad that the vote he was most proud of from his time in the Colorado Legislature was the Denver-Boulder Turnpike, which opened in 1952.
 NIST (then the National Bureau of Standards) and Rocky Flats were opened in the early '50s; Beech Aircraft and Ball Aerospace in the mid-late '50s; NCAR in the early 1960s.
says you could get a home loan in Martin Acres for $700 down in 1950.
 My dad's family moved into a brand new house on Carnegie Drive in 1963. My dad said they could've gotten a better deal elsewhere, but his mom wanted a brand new house so she wouldn't have to clean it before moving in, a luxury she'd longed for in the Army.
 IBM's presence on the Diagonal starting in the mid-60s is a fantastic example of "Of course everyone will drive to work."
 My parents paid $80,000 cash for a 4-bedroom house in 1980. In the late '90s, houses in our neighborhood were selling for $400,000.
[Bonus footnote] Boulder was a dry town from 1907 to 1967, so the British ideal of a pub in every neighborhood was illegal when most Boulder subdivisions were built.