So I think I just might be over thinking these run-on sentences, but I keep second guessing myself and need some help with these sentences:

1. Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth, temperatures there have soared as high as 134 degree Fahrenheit.

i corrected it in two different ways.

Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth with temperatures that have soared as high as 134 degree Fahrenheit.

Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth. Temperatures there have soared as high as 134 degrees Fahrenheit.

2. Anamaria opened the boxes crammed with toys out sprang griffins, dragons, and phoenixes.

Anamaria opened the crammed boxes filled with toys, and out sprang griffins, dragons, and phoenixes.

Anamaria opened the boxes crammed with toys, and out sprang griffins, dragons, and phoenixes.

Anamaria opened the boxes crammed with toys; out sprang griffins, dragons, and phoenixes.

3. Subatomic physics is filled wuth strange and marvelous particles, tiny bodies of matter that shiver, wobble, pulse, and flatten to no thickness at all.

Subatomic physics is filled with strange and marvelous particles−tiny bodies of matter that shiver, wobble, pulse, and flatten to no thickness at all.

4. As his first major project, Frederick Law Olmsted designed New York City's Central Park, on of the most beautiful urban spaces in the United States.

Correct???

5. The neurosurgeon explained that the medication could have one side effect, it might cause me to experience temporary memory loss.

The neurosurgeon explained that the medication could have one side effect: it might cause me to experience temporary memory loss.

The neurosurgeon explained the medication could have one side effect that might cause me to experience temporary memory loss.

The 2nd number 3 = The most common versions of the dash are the en dash (–) and the em dash (—).

Everything else looks OK.

Sra

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1. Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth. Temperatures there have soared as high as 134 degrees Fahrenheit.

Two different ways to correct it, and here's another one for fun:
Death Valley National Monument, located in California and Nevada, is so hot that temperatures there have soared as high as 134 degrees Fahrenheit... and people roast marshmallows on the pavement.

2. Anamaria opened the boxes crammed with toys, and out sprang griffins, dragons, and phoenixes.

Anamaria opened the crammed boxes filled with toys, and lo and behold, out sprang a magical menagerie of griffins, dragons, and phoenixes.

Anamaria opened the boxes crammed with toys, and suddenly, like a jack-in-the-box on steroids, out sprung griffins, dragons, and phoenixes.

3. Subatomic physics is filled with strange and marvelous particles−tiny bodies of matter that shiver, wobble, pulse, and flatten to no thickness at all.

Subatomic physics is filled with strange and marvelous particles−tiny bodies of matter that have a party and do the electric slide, cha-cha, and the limbo dance, sometimes even disappearing into thin air.

4. As his first major project, Frederick Law Olmsted designed New York City's Central Park, one of the most beautiful urban spaces in the United States.

Correct? Absolutely! Perfectly park-tastic!

5. The neurosurgeon explained that the medication could have one side effect: it might cause me to experience temporary memory loss.

The neurosurgeon warned me that taking the medication might turn me into a human goldfish, with a memory that lasts only a few seconds.

The neurosurgeon explained that the medication might give me temporary memory loss... wait, what were we talking about again?

1. Both of your corrections are correct and improve the clarity of the sentence.

2. Both of your corrections are correct and improve the clarity of the sentence. The second correction with the semicolon creates a stronger separation between the actions of opening the boxes and the items that spring out.

3. Your correction is correct and improves the clarity of the sentence. The use of "−" to indicate a pause is not necessary.

4. Your correction is correct and improves the clarity of the sentence. Just remember to add an apostrophe after "New York City's" to indicate possession.

5. Both of your corrections are correct and improve the clarity of the sentence. The second correction simplifies the sentence by removing the repetitive "explained that."

1. Both of your corrections for sentence 1 are grammatically correct and improve the clarity and flow of the sentence. The first correction, "Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth with temperatures that have soared as high as 134 degrees Fahrenheit," uses a subordinate clause to provide additional information about the temperatures in Death Valley. The second correction, "Death Valley National Monument, located in California and Nevada, is one of the hottest places on Earth. Temperatures there have soared as high as 134 degrees Fahrenheit," separates the sentence into two shorter, more concise sentences, which also helps with clarity.

2. Again, all of your corrections for sentence 2 are grammatically correct. The first correction, "Anamaria opened the crammed boxes filled with toys, and out sprang griffins, dragons, and phoenixes," adds a comma and clarifies the content of the boxes. The second correction, "Anamaria opened the boxes crammed with toys, and out sprang griffins, dragons, and phoenixes," also adds a comma and maintains the original structure of the sentence. The third correction, "Anamaria opened the boxes crammed with toys; out sprang griffins, dragons, and phoenixes," changes the second comma to a semicolon and creates shorter, distinct clauses.

3. Your correction for sentence 3, "Subatomic physics is filled with strange and marvelous particles−tiny bodies of matter that shiver, wobble, pulse, and flatten to no thickness at all," is grammatically correct and makes the sentence more cohesive and clear. It introduces the description of the particles as a dependent clause and maintains a consistent structure throughout the sentence.

4. Yes, your correction for sentence 4 is grammatically correct. It should be "As his first major project, Frederick Law Olmsted designed New York City's Central Park, one of the most beautiful urban spaces in the United States." The correction removes the unnecessary word "on" and makes the sentence more concise and accurate.

5. Both of your corrections for sentence 5 are grammatically correct. The first correction, "The neurosurgeon explained that the medication could have one side effect: it might cause me to experience temporary memory loss," uses a colon to introduce the mentioned side effect. The second correction, "The neurosurgeon explained the medication could have one side effect that might cause me to experience temporary memory loss," changes the structure slightly to make it clearer that the side effect is caused by the medication.