Did they actually have "mushroom cloud tourist attraction" to Nevada Test Site in the 1950s?

There's an important social aspect to this that hasn't been addressed so far. Until August 1949, when the USSR performed its first nuclear test, the atom bomb was the source and symbol of the USA's status as the sole superpower. After that, the improvement of atom bombs and development of hydrogen bombs was an important part of American actions to maintain their status.

Such things tend to be viewed vary positively in the American style of patriotism, and dangers from them tend to be ignored, at least for a while. Tom Lehrer satirised the matter rather well in 1953.

I just wanted to add this link to what has been said. Yes, the mindset was that radiation from the bombs was not as dangerous. If you want proof of there, here is a youtube video of five army guys STANDING AT GROUND ZERO during an air burst. (The missile explodes several miles directly above them)

In fact, the army did drills where troops would hunker down near ground zero, to get the troops used to the idea of fighting during a nuclear war.

For another account on the (this time informed) contemporary attitude, read Richard Feynman's book Los Alamos from Below published here in full or quoted here.

The gist is, he figured that at 20 miles distance he would be safe behind a car's windshield and would see more without dark glasses.

... But just a few minutes before it was supposed to go off the radio started to work, and they told us there was 20 seconds or something to go, for people who were far away like we were. Others were closer, 6 miles away.

They gave out dark glasses that you could watch it with. Dark glasses! Twenty miles away, you couldn't see a damn thing through dark glasses. So I figured the only thing that could really hurt your eyes - bright light can never hurt your eyes - is ultraviolet light. I got behind a truck windshield, because the ultraviolet can't go through glass, so that would be safe, and so I could see the damn thing. OK.

Time comes, and this tremendous flash out there is so bright that I duck, and I see this purple splotch on the floor of the truck. I said, “That ain't it. That's an after-image.” So I look back up, and I see this white light changing into yellow and then into orange. The clouds form and then they disappear again; the compression and the expansion forms and makes clouds disappear. Then finally a big ball of orange, the center that was so bright, becomes a ball of orange that starts to rise and billow a little bit and get a little black around the edges, and then you see it's a big ball of smoke with flashes on the inside of the fire going out, the heat. ...

In regards the secondary question, namely

Am I missing something here?

Yes; absolutely. You have neglected both the shielding effect of the 65 miles of air between Las Vegas and the bomb explosions, and the fact that the actual radiation intensity falls off as the square of the distance.

The study The Children of Atomic Bomb Survivors: A Genetic Study. by National Research Council (US); National Academy of Sciences (US); Neel JV, Schull WJ, editors. notes for Hiroshima:

On the other hand, both from these two curves and on the basis of our own observations regarding the shape of the distance-dosage curve, it seems likely that persons at distances in excess of 3,000 meters received little if any radiation. [right above Figure 4.3]

Air Shielding Attenuation

Consider the air-shielding effect first. To a first approximation the shielding material is irrelevant, except so far as different materials have different densities. The shielding effect can be approximated by calculating the material density times the thickness. For Hiroshima survivors beyond 3,000 metres I will assume:

• 3000 metres of air at 1.2754 kg/m³ = 3,826 kg/m²

• 30 metres (1%) of pine at 420 kg/m³ = 12,600 kg/m²

• total shielding effect = 16,400 kg/m²

For Las Vegas Bomb Tourists assume:

• 65 miles * 1600 m/mile at 1.2754 kg/m³ = 248,700 kg/m²; roughly 15 times that of Hiroshima survivors just outside the 3,000 metres "no significant radiation" suffered radius.

Distance Attenuation

At a distance of 65 miles = 104,000 metres, roughly 34.7 times as far from the blast centre as the Hiroshima survivors beyond 3,000 metres, the radiation reaching Las Vegas *Bomb Tourists has been distance-attenuated 34.7² = 1200 times as much as for the Hiroshima survivors outside the 3,000 metres radius.

Total Attenuation (of Direct Radiation)

While the precise calculation is undoubtedly more complex, certainly both attenuation effects must be regarded as combining. This means that the direct radiation experienced by Las Vegas Bomb Tourists will have been somewhere in between 1/1200 = 0.08% and 1/(1200*15) = 0.0005% that experienced by Hiroshima survivors outside the 3,000 metres "experienced no significant radiation" radius.

Yes, this analysis ignores the effects of radioactive fallout - that calculation being so intrinsically dependent on meteorological particularities of each blast. However I hope the above makes clear that the distance of Las Vegas from the test site was far more than sufficient to protect occasional visitors. Permanent residents might be another story - but that's a different question.

From comments below, and expanded

Yield Considerations

The largest nuclear device ever detonated was the Russian Tsar Bomba, at 50 Mega Tons (and it was s research device, not an intended weapon). The largest device ever designed and detonated by the U.S. was the MK-41 at 25 Mega Tons: about 1600 times the Hiroshima bomb (15 Kilo Tons of TNT).

For back-of-the-envelope considerations, even the 1600 times yield increase from Hiroshima is much smaller than the 1200 * 15 = 18,000 times attenuation provided by sheer distance from the bomb blast.

However all such devices are thermonuclear, not pure atomic, devices with a second fusion stage triggered by a primary fission stage (and possibly also incorporating a third, fission) stage.

As thermonuclear weapons represent the most efficient design for weapon energy yield in weapons with yields above 50 kilotons of TNT (210 TJ), virtually all the nuclear weapons of this size deployed by the five nuclear-weapon states under the Non-Proliferation Treaty today are thermonuclear weapons using the Teller–Ulam design.

From here any discussion of radiation (and fallout) profile is very specific for each particular bomb design - by intent. One must distinguish between the different effects and penetrating power of all of:

• Alpha particles - high energy helium nuclei;

• Beta particles - high energy electrons (and possibly positrons);

• Gamma rays - high energy photons;

• High (and low!) energy neutrons; and

• Radioactive fallout such as strontium-90 (a long-term environmental hazard only unless one is immersed directly in the speed of weather only disbursed radioactive cloud, and even that is constrained to spread roughly as the square of distance traveled).

However energy is energy; it spreads outwards from an epicentre; and the inherently geometric effects described above cannot be avoided.

Yes. There are many articles supporting this claim. Here's one from Bloomberg:

For four decades, the U.S. Department of Energy tested more than a thousand nuclear devices at the Nevada Test Site, a desert expanse just 65 miles northwest of Las Vegas. The 1951 detonation of a warhead 1,060 feet over the desert floor marked the beginning of the above-ground trials, whose famous mushroom clouds were easily visible from the nearby tourist magnet.

“They would light up the sky,” says Allen Palmer, executive director of the National Atomic Testing Museum. “It turned night into day.”

In true Las Vegas style, the city capitalized on the atomic spectacle. The Chamber of Commerce printed up calendars advertising detonation times and the best spots for watching. Casinos like Binion’s Horseshoe and the Desert Inn flaunted their north-facing vistas, offering special “atomic c**ktails” and “Dawn Bomb Parties,” where crowds danced and quaffed until a flash lit the sky. Women decked out as mushroom clouds vied for the “Miss Atomic Energy” crown at the Sands. “The best thing to happen to Vegas was the Atomic Bomb,” one gambling magnate declared.

If you're more into videos, you might like this Smithsonian article.